Historic Properties and Federal
May 5, 2023
Responsibilities: An Introduction to Section
Mark K. DeSantis
106 Reviews
Analyst in Natural
Resources Policy
The National Historic Preservation Act (NHPA; 54 U.S.C §§300101 et seq.), as amended,

created a process for federal agencies to follow when projects may affect certain historic
resources. Among its various provisions, Section 106 of the NHPA requires federal agencies to

“take into account” the effects their actions may have on historic properties. Such properties
include any prehistoric or historic districts, sites, buildings, structures, or objects that are listed or are eligible for listing on
the National Register of Historic Places. Actions subject to review under the NHPA, referred to as federal undertakings,
include actions directly undertaken, funded, or permitted by a federal agency, as well as actions administered by state or local
governments pursuant to a delegation or approval by a federal agency. The process of evaluating the effects of federal
undertakings on historic properties is referred to as a Section 106 review.
Section 106 reviews generally follow a four-step process: (1) initiation, in which the agency determines whether the action is
an undertaking subject to review; (2) identification of historic properties in the area of potential effects; (3) assessment of
whether the action would cause adverse effects to historic properties; and (4) resolution between parties on steps to address
any adverse effects. Throughout the Section 106 process, federal agencies must consult with various entities—such as the
relevant state historic preservation officer (SHPO) or tribal historic preservation officer (THPO)—to determine whether
historic properties have been identified and to craft potential solutions to avoid, minimize, or mitigate adverse effects on
historic properties.
Overview of Section 106 Review Steps

Source: Congressional Research Service, using 36 C.F.R. Part 800.
The NHPA does not require an agency to select the option that best avoids adverse effects. Instead, the implementing
regulations for Section 106, promulgated by the Advisory Council on Historic Preservation, outline potential ways to address
situations in which adverse effects may occur. For example, the agency and the SHPO and/or THPO may enter into a
memorandum of agreement (MOA) that details a plan to minimize damage to the historic property. In practice, the majority
of Section 106 reviews for undertakings that adversely affect historic properties result in an MOA. If the parties cannot reach
an agreement, regulations provide for the agency or other parties involved to formally terminate the consultation process.
Formal termination also may fulfill an agency’s responsibilities under Section 106.
Not every federal undertaking will require an agency to go through every step of this process. For example, agencies may use
alternative methods—known as program alternatives—to meet their obligations under Section 106. As a result, the time and
resources required to comply with Section 106 vary depending on the scale and complexity of the project in question.
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Historic Properties and Federal Responsibilities: An Introduction to Section 106 Reviews

he National Historic Preservation Act (NHPA; 54 U.S.C §§300101 et seq.), as amended,
created a process for federal agencies to follow when projects may affect a historic
T property.1 This process is found in Section 106 of the NHPA and thus is known as a
Section 106 review.2 Section 106 and its implementing regulations require federal agencies to
review the potential impacts of their actions on historic sites and consult with interested parties to
seek ways to avoid, minimize, or mitigate any adverse effects. Although the NHPA does not
require an agency to select the option that best avoids adverse effects, the regulations outline
potential ways to resolve situations in which adverse effects may occur, such as through a
memorandum of agreement among the agency and other stakeholders on a plan to minimize
damage to the historic property.
Issues related to Section 106 of the NHPA are of regular interest to Members of Congress and
other stakeholders. These questions may include whether or to what degree the process has been
effective in protecting or mitigating damage to historic properties, the adequacy of federal agency
consultation procedures, and perceived inefficiencies in the process that some view as delaying
certain projects. In addition, at times, Congress has considered legislation that would exempt or
reduce agency obligations under Section 106 for certain actions.3
This report addresses procedural questions that legislators have posed regarding Section 106,
particularly in the context of congressional oversight of agency compliance actions. Specifically,
the report provides an overview of the standard procedures for complying with Section 106 as
outlined in federal regulations found at 36 C.F.R. Part 800.4 Some Members also have expressed
interest in better understanding the roles and responsibilities of the various parties involved in the
Section 106 process. As such, the report describes the various steps required of federal agencies
and other parties throughout the Section 106 process. It also highlights key terms defined in
statute, agency regulations, and guidance to help in understanding compliance with Section 106
requirements. This report does not address proposals or options to amend or alter the Section 106
requirements.
Key Definitions
The NHPA and implementing regulations promulgated by the Advisory Council on Historic
Preservation (ACHP; see definition below) use various terms specific to the Section 106 review
process. Familiarity with these terms is helpful in understanding Section 106 review and the roles
and responsibilities of the various parties throughout the process. Selected key terms used
throughout this report are highlighted below:
 Advisory Council on Historic Preservation. The NHPA authorized the ACHP to
oversee federal agencies’ implementation of Section 106. Created by NHPA, the
ACHP is an independent agency comprising federal, state, and tribal government
members, as well as experts in historic preservation and members of the public.5

1 National Historic Preservation Act (NHPA; 54 U.S.C. §§300101 et seq.). For more information on the NHPA, see
CRS Report R45800, The Federal Role in Historic Preservation: An Overview, by Mark K. DeSantis.
2 54 U.S.C. §306108.
3 For example, see H.R. 8168 and H.R. 940 in the 117th Congress, both of which would have exempted certain forest
management activities from review under Section 106.
4 These regulations are promulgated by the Advisory Council on Historic Preservation (ACHP).
5 54 U.S.C. §§304101 et seq.
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Through its authority under the NHPA, the ACHP promulgated regulations for
the Section 106 process.
 Agency/Lead Agency. The federal agency, or lead agency if more than one agency
is involved, is the entity with designated responsibility for compliance with
Section 106. When multiple federal agencies are involved in a proposed federal
action subject to Section 106, some or all of the agencies may designate a lead
agency to act on their behalf, fulfilling their collective responsibilities under the
law.6 Although there are instances in which certain nonfederal entities (see below
regarding an applicant for federal assistance, permits, or licenses) may be asked
to carry out some of the tasks for completing a Section 106 review, the federal
agency remains responsible for all findings and determinations under the law.
 Applicant. The applicant is the entity applying for federal funding or for a federal
permit, license, or other approval subject to Section 106 review. Regulations
allow federal agencies to authorize an applicant (or group of applicants) to carry
out certain Section 106 requirements. Under such an authorization, an applicant
may be allowed to consult with the state or tribal historic preservation officer
(SHPO/THPO; see below) in identifying and evaluating historic properties and in
assessing effects of the proposed undertaking. The agency has discretion in
determining what activities an applicant may be authorized to conduct. The
agency remains responsible for all findings and determinations made throughout
the review process, as well as for any government-to-government relationships
with tribes.7
 Area of Potential Effects (APE). The APE is the geographic area or areas within
which an undertaking may directly or indirectly cause alterations in the character
or use of historic properties, if any such properties exist.8 The APE is influenced
by the scale and nature of an undertaking and may be different for different kinds
of effects caused by the undertaking.
 Historic Property. A historic property is any prehistoric or historic district, site,
building, structure, or object included on, or eligible for inclusion on, the
National Register of Historic Places (National Register), including artifacts,
records, and material remains relating to the district, site, building, structure, or
object.9 The NHPA was amended in 1976 to include the phrase “or eligible for
inclusion on” the National Register. 10 Prior to that, Section 106 covered only
properties already listed on the National Register.
 State/Tribal Historic Preservation Officer. The SHPO is the state’s lead authority
for historic preservation and “reflects the interests of the State and its citizens in
the preservation of their cultural heritage.”11 When tribal properties are at stake,
federal agencies must consult with the THPO. The main responsibilities of the
SHPO/THPO in the Section 106 process are to “advise and assist” federal
agencies in carrying out their responsibilities and to review agency findings

6 36 C.F.R. §§800.2(a)(2) and 800.16(b).
7 36 C.F.R. §800.2(c)(4).
8 36 C.F.R. §800.16(d).
9 54 U.S.C. §300308.
10 P.L. 94-422.
11 36 C.F.R. §800.2(c)(1).
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regarding the identification and assessment of an undertaking’s impacts on
historic properties.
 Undertaking. An undertaking is a “project, activity, or program funded in whole
or in part under the direct or indirect jurisdiction of a Federal agency.”12
Undertakings include both actions directly undertaken, funded, or permitted by a
federal agency and actions administered by state or local governments pursuant
to a delegation or approval by a federal agency.
Overview of Section 106
Similar to other federal laws intended to preserve or protect natural or cultural resources, the
NHPA’s directives apply to federal agency actions. In particular, Section 106 requires federal
agencies to “take into account” the effect their actions may have on historic properties. Pursuant
to the NHPA, the Section 106 process is to be concluded before the expenditure of any federal
funds or issuance of any federal license.13
Federal regulations outline a four-step process for agencies to comply with Section 106
requirements:
1. Initiation. The agency determines whether a proposed action is an undertaking
and, if so, whether the undertaking is a type of activity that has the potential to
cause effects on historic properties.
2. Identification. The agency identifies the appropriate consulting parties, the
project’s APE, and whether any historic properties are located within the project
area.
3. Assessment. The agency determines whether the proposed action would
adversely affect the historic properties in question.
4. Resolution. If possible, the agency and stakeholders enter into an agreement
detailing how the agency plans to address any adverse effects to historic
properties.
The following sections describe standard procedures for complying with these steps. Not every
federal undertaking necessarily requires an agency to complete every step. The majority of
federal actions reviewed annually either do not involve historic properties or are actions that
would not adversely affect historic properties.14 In these instances, agency compliance with
Section 106 may be satisfied in one or two steps. In addition, agencies often coordinate Section
106 compliance with other federal review processes, such as those required by the National
Environmental Policy Act (NEPA), the Archaeological Resource Protection Act, and the Native
American Graves Protection and Repatriation Act.15 In particular, regulations encourage federal

12 54 U.S.C. §300320.
13 54 U.S.C. §306108.
14 A study commissioned by the National Trust for Historic Preservation in 2010 indicated that of the 114,000
eligibility actions reviewed annually, approximately 85% were found not to involve historic properties. According to
the report, this number represents the number of properties reviewed for eligibility during a project’s Section 106
review and not the number of federal undertakings reviewed. Information is based on data provided by the National
Park Service. Leslie E. Barras, “Summary,” in Section 106 of the National Historic Preservation Act: Back to Basics,
2010, p. 5.
15 These laws are codified as follows: National Environmental Policy Act (NEPA; 42 U.S.C. §§4321 et seq.);
Archaeological Resource Protection Act (16 U.S.C. §§470aa et seq.); and Native American Graves Protection and
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agencies to use their broad environmental review process, carried out under NEPA, as an
“umbrella” compliance process.16 However, compliance with reviews required under one or more
other statutes does not substitute for an agency’s compliance with the requirements under Section
106.
Certain scenarios or types of actions also may result in agencies taking alternate procedural steps
to comply with NHPA requirements, not all of which are reflected in this report. For example,
federal regulations allow agencies, with agreement from relevant parties, to compress or expedite
multiple steps of the process in certain instances (see text box entitled “Section 106 Program
Alternatives”).17 The NHPA also provides an exception to the Section 106 requirements in certain
emergency situations, authorizing the Secretary of the Interior to issue regulations waiving all or
part of the process “in the event of a major natural disaster or an imminent threat to the national
security.”18 Finally, the NHPA applies different standards of protection when the undertaking has
the potential to affect a property designated as a national historic landmark (NHL).
In general, the time needed—and the analysis required—to comply with Section 106 is contingent
on the scale and complexity of the project in question. As a result, it is difficult to determine the
length of time required for an agency to comply with Section 106 for a proposed undertaking.
Although each scenario may be unique, this report is intended to provide Members and
stakeholders with a basic understanding of the procedural requirements of Section 106.
Understanding Consultation: The Basics
Consultation is the backbone of the Section 106 process. It is an interactive process that may occur at various
points during a Section 106 review and requires an agency (or authorized applicant) to consider input from
identified consulting parties. Specifically, consultation is defined as the “process of seeking, discussing, and
considering the views of other participants, and, where feasible, seeking agreement with them regarding matters
arising in the Section 106 process” (36 C.F.R. §800.16(f)).
Consultation can involve both informal and formal communication, and the Advisory Council on Historic
Preservation (ACHP) encourages agencies to begin consultation early in the project planning process. Although
agencies may col aborate with and seek informal input from consulting parties throughout the Section 106
process, federal regulations specifically require agencies to consult with state and/or tribal historic preservation
officers at certain points. These consultations are required when the agencies are identifying historic properties
potentially affected by the undertaking, assessing whether effects may be adverse in nature, and seeking ways to
avoid, minimize, or mitigate any adverse effects on identified historic properties.
Section 106 regulations do not prescribe exactly how the consultation process must proceed, nor do they set an
expected timeline for resolution of consultative interactions. As a result, the specific consultation process may
differ from project to project. The general process involves parties sharing information so the agency may make a
well-informed decision regarding how to proceed with the project. Section 106 review does not require a federal
agency to take a prescribed action or meet a specific preservation outcome.
Step 1: Initiation
Agencies must determine whether or when a particular action triggers Section 106 review. Not
every action involving a federal agency or federal funds must undergo review and consultation
under Section 106. In addition, some federal agencies may have agreements that allow for
deviations from the standard compliance procedures outlined below (see “Section 106 Program

Repatriation Act (5 U.S.C. §§3001 et seq.).
16 Regulations for the coordination of the Section 106 Process with NEPA can be found at 36 C.F.R. §800.8.
Discussion of NEPA as an “umbrella” compliance process can be found at ACHP, “Integrating NEPA and Section
106,” at https://www.achp.gov/integrating_nepa_106.
17 36 C.F.R. §800.3(g).
18 54 U.S.C. §306112.
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Alternatives” text box, below). Agencies typically make these step 1 determinations without
consultation from outside parties. Figure 1 illustrates the process of how such determinations
may be made at this stage.
Figure 1. Initiation

Source: Congressional Research Service (CRS), using 36 C.F.R. §800.3.
Is the Proposed Action an Undertaking?
The Section 106 process is triggered by a federal undertaking. Under the act, an undertaking is
defined as “a project, activity, or program funded in whole or in part under the direct or indirect
jurisdiction of a Federal agency” (see “Key Definitions”).19 In 1992, Congress amended the
definition to include the following examples of types of projects that constitute undertakings:
 Those carried out by or on behalf of an agency
 Those carried out with federal financial assistance
 Those requiring a federal permit, license, or approval
 Those subject to state or local regulation administered pursuant to a delegation or
approval by a federal agency20
In general, Section 106 does not apply to actions taken entirely by state, local, or private entities
(i.e., actions taken without the use of federal funding, federal permits, or some other federal
nexus).
Does the Undertaking Have the Potential to Affect Historic Properties?
Once an agency determines a proposed federal action is an undertaking, the agency determines
whether the action is a type of activity that has the potential to cause effects on historic

19 54 U.S.C. §300320.
20 P.L. 102-575, §4019. Amendments codified at 54 U.S.C. §300320.
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properties.21 At this stage, the agency is not required to determine whether such effects may be
adverse (i.e., alter the characteristics of a property in a way that would diminish its historical
integrity) or whether the undertaking is likely to affect any specific historic properties. Instead,
the agency makes a determination as to the nature of the federal action and whether additional
Section 106 requirements might apply.22 If an agency determines the proposed undertaking does
not have the potential to affect historic properties, the agency has no further obligations under
Section 106.
Section 106 Program Alternatives
During the initiation stage of the Section 106 process, regulations direct agencies to determine whether the
proposed undertaking is subject to a program alternative established under 36 C.F.R. §800.14. Program alternatives
are alternative methods available to federal agencies to meet their obligations under Section 106. These program
alternatives allow federal agencies to work with the Advisory Council on Historic Preservation (ACHP) to tailor
the Section 106 process to meet their needs. The program alternatives vary in the extent to which they may
substitute for the standard compliance procedures, which are found in 36 C.F.R. Subpart B.
The available program alternatives include (1) alternate procedures, (2) programmatic agreements, (3) exempted
categories, (4) standard treatments, and (5) program comments.
The first option—development of alternate procedures—allows an agency to whol y or partially replace the ACHP’s
standard regulations with its own procedures, whereas some other alternatives apply to specific aspects of the
standard procedures or to specific agency programs or categories of actions. Programmatic agreements allow
agencies to negotiate agreements with the ACHP to govern Section 106 compliance for an individual agency
program, complex project, or group of related undertakings (36 C.F.R. §800.14(b)). According to the ACHP,
programmatic agreements are the most commonly used of the five program alternatives. Requirements applicable
to exempted categories allow the ACHP or an affected agency to propose a program or category of activities that
wil be exempted from Section 106 review, if such actions have foreseeable effects on historic properties that are
likely to be minimal and not adverse (36 C.F.R. §800.14(c)). Provisions for standard treatments allow the ACHP, on
its own initiative or at another party’s request, to establish a standard method for treating a category of historic
properties, a category of undertakings, or a category of effects on historic properties (36 C.F.R. §800.14(d)).
Finally, program comments allow the ACHP, at an agency’s request or on its own initiative, to comment on a
category of undertakings in lieu of conducting individual reviews of undertakings as outlined in this report (36
C.F.R. §800.14(e)).
When an agency determines a proposed action is an undertaking and is subject to Section 106, the appropriate
agency official also wil determine whether the action is covered by any program alternative. Regulations require
agencies to fol ow the program alternative if it applies. For further discussion of the program alternatives, see
ACHP, “Program Alternatives,” at https://www.achp.gov/program_alternatives.
Source: 36 C.F.R. §800.14.
Step 2: Identification
If an agency determines an undertaking has the potential to affect historic properties, the agency
enters the second phase of the Section 106 process. At this stage, the agency (or authorized
applicant) is responsible for identifying and contacting the consulting parties, determining and
defining the project’s APE, and identifying which historic properties located within the APE the
project might affect (see Figure 2).

21 36 C.F.R. §800.3(a)(1).
22 The ACHP provides examples of the types of federal undertakings that would not affect historic properties, including
Social Security payments, student loans, or grants for libraries to acquire books. See ACHP, “Section 106 Regulations
Section-by-Section Questions and Answers Synopsis,” at https://www.achp.gov/digital-library-section-106-landing/
section-106-regulations-section-section-questions-and-answers.
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Figure 2. Identification

Source: CRS, using 36 C.F.R. §§800.2(c), 800.3(c)-(f) and §800.4.
Notes: Although not indicated separately in this figure, authorized applicants may undertake some of an agency’s
identification and consultation requirements listed here (see definition of applicant in “Key Definitions”). For
more information on the dispute process, see Figure A-1.
Who Are the Consulting Parties?
If an agency’s undertaking may affect historic properties, the next step in the Section 106 process
is to identify the appropriate consulting parties. Under the NHPA, Section 106 consultation is an
interactive process in which an agency evaluates an undertaking’s effects on a historic property
with input from relevant stakeholders. These stakeholders—referred to as consulting parties in
regulations—are the SHPO and/or THPO and can include applicants for a relevant license or
permit, representatives of local government, affected Indian tribes or Native Hawaiian
organizations, or other parties with a demonstrated interest in the undertaking.23
What Is the Area of Potential Effects?
The next step is to identify the area that the project may affect, known as the area of potential
effects (see “Key Definitions”). Agencies identify the APE in consultation with the SHPO or

23 36 C.F.R. §800.2(c). The regulations require that the agency “shall invite any local governments” (36 C.F.R.
§800.3(f)(1)) and “make a reasonable and good faith effort to identify Indian tribes and Native Hawaiian organizations”
(36 C.F.R. §800.3(f)(1)). The NHPA defines Indian tribe to include Alaska Native Villages and Corporations). Not all
tribes or Native Hawaiian organizations have a designated tribal historic preservation officer. Regulations still require
agencies to consult with a representative designated by any Indian tribe or Native Hawaiian organization that attaches
religious and cultural significance to historic properties that an undertaking may affect.
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THPO.24 The APE determination may affect the contents of a Section 106 review, as it determines
the review’s scope. Only those properties within the APE are evaluated for project impacts.
The APE is not synonymous with the geographic footprint of the project in question. Instead, the
APE is intended to reflect the area where a project could affect historic properties, both directly
and indirectly. Although regulations do not define what constitutes an indirect effect, the criteria
for assessing adverse effects (see section, “Will the Undertaking Potentially Cause an Adverse
Effect on Historic Properties?”) include “reasonably foreseeable effects caused by the
undertaking that may occur later in time, be farther removed in distance, or be cumulative.”25 As a
result, an APE may include areas that are not contiguous with the project area and agencies may
define different APEs for different kinds of effects.26 In addition, the APE(s) can be refined or
altered as planning and analysis progress.
Are There Historic Properties Located Within the APE?
After identifying the APE for a particular undertaking, the agency identifies any historic
properties in the APE in consultation with the SHPO and/or THPO. Historic properties include
those listed on the National Register and those eligible to be listed on the National Register (see
“Key Definitions”). Eligible properties may be harder to identify than listed properties, as there
may be more limited documentation of eligible properties’ location, significance, or association.
Regulations state that federal agency officials shall make a “reasonable and good faith effort” to
identify historic properties.27 Although some level of effort is required to demonstrate that the
“reasonable and good faith” identification standard is met, regulations do not prescribe any one
methodology.28 The regulations direct agencies to consider factors such as “past planning,
research and studies, the magnitude and nature of the undertaking and the degree of Federal
involvement, the nature and extent of potential effects on historic properties, and the likely nature
and location of historic properties within the area of potential effects.”29 The identification
process also may include cultural resource surveys within the APE, primary research,
consultations, and other activities.30 Typically, agencies ask the SHPO/THPO to help identify
such properties. The agency also may consult other parties for assistance with identifying such
properties.
If the agency concludes there are no historic properties within the APE, the agency notifies the
relevant consulting parties and provides documentation for the finding. As noted above (see
agency/lead agency in “Key Definitions”), even in instances when nonfederal entities conduct
identification activities, the federal agency is ultimately responsible for issuing all findings and

24 36 C.F.R. §800.4(a)(1).
25 36 C.F.R. §800.5(a)(1).
26 For example, if a project were to involve excavation or construction, there may be one area of potential effects (APE)
for direct disturbances to qualified archaeological resources located on the construction site and a different APE for
indirect impacts to aboveground resources subject to visual, audible, vibratory, or atmospheric effects (e.g., if
vibrations from excavation cause the foundations of nearby historic buildings to crack).
27 36 C.F.R. §800.4(b)(1).
28 The ACHP has issued guidance for understanding the “reasonable and good faith” standard. See ACHP, Meeting the
“Reasonable and Good Faith” Identification Standard in Section 106 Review, May 2018, at https://www.achp.gov/
sites/default/files/guidance/2018-05/reasonable_good_faith_identification.pdf.
29 Ibid.
30 For undertakings primarily initiated by nonfederal entities (e.g., authorized applicants), these tasks are typically
completed by private consultants with permits to conduct surveys on federal and state lands. For undertakings initiated
by a federal agency, the agency in question typically completes such tasks.
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determinations. Upon receipt of the finding and associated documentation, the consulting parties
have 30 calendar days to object to the agency’s finding. If the consulting parties agree with the
agency finding or do not respond within the 30-day window, the Section 106 process is complete
and the agency’s obligations have been fulfilled.31
If the agency determines there are historic properties that may be affected by the undertaking, the
agency issues a formal finding indicating as such, notifies all consulting parties, and proceeds to
“Step 3: Assessment.”32
Does a Consulting Party Disagree with the Agency Finding of No Historic
Properties?
Disagreements between the agency and consulting parties at this stage often pertain to questions
of eligibility for properties that are not listed on the National Register. In such instances, one or
more of the consulting parties may take the position that a specific property within the APE meets
the eligibility criteria of a historic property and therefore requires the agency to consider potential
effects of the proposed undertaking.33 Reasonable parties may disagree as to how the eligibility
criteria should be applied. Parties have debated what constitutes a “reasonable and good faith
effort” by federal agencies (or the applicable entity conducting such activities) to identify historic
properties. Questions of whether sufficient efforts were made to identify eligible properties
frequently arise, particularly within the context of identifying cultural resources of Indian tribes
due to tribal concerns about revealing sacred sites.34
If a consulting party objects to the agency’s finding of no historic properties, the agency has two
options: (1) continue consultation with the SHPO/THPO or other relevant parties or (2) submit
findings directly to the ACHP for an opinion.35 For an overview of how agencies and consulting
parties address disagreements, see the Appendix.
If the agency—through consultation with the SHPO/THPO or pursuant to an opinion from the
ACHP—reverses an initial finding of no historic properties, the agency proceeds to “Step 3:
Assessment.”
Step 3: Assessment
The third step in the Section 106 process requires the agency (or authorized applicant) to
determine whether the project might affect identified historic properties and if any such effects
would be adverse in nature. The agency does so in consultation with other participants (see
Figure 3).

31 36 C.F.R. §800.4(c)(1).
32 36 C.F.R. §800.4(d)(2).
33 The criteria applied to evaluate properties for the National Register of Historic Places are located at 36 C.F.R. §60.4.
To be eligible for listing on the register, and thus identified as a historic property under NHPA, a property must be
linked to history by association to significant events or persons; by possessing distinct characteristics of an era; or by
having integrity of location, materials, workmanship, or association.
34 Section 106 regulations caution agencies regarding this potential problem, advising that “an Indian tribe or Native
Hawaiian organization may be reluctant to divulge specific information regarding the location, nature, and activities
associated with such sites” (36 C.F.R. §800.4(a)(4)).
35 36 C.F.R. §800.5(c)(2).
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Figure 3. Assessment

Source: CRS, using 36 C.F.R. §800.5.
Notes: Although not indicated separately in this figure, authorized applicants may undertake some of an agency’s
identification and consultation requirements listed here (see definition of applicant in “Key Definitions”).
Will the Undertaking Potentially Cause an Adverse Effect on Historic
Properties?
Once the agency (or applicable entity) identifies any historic properties located within the APE, it
determines whether the undertaking may have an adverse effect on those properties. It is possible
for an action to have an effect on a historic property that is not considered adverse in nature. 36
Only actions expected to have an adverse effect on historic properties require additional review
under Section 106.
The Section 106 regulations provide guidance as to which effects are considered adverse. For
example, alterations in “any of the characteristics of a historic property that qualify the property
for inclusion in the National Register” constitute adverse effects.37 Specifically, agencies must
consider impacts to the “integrity” of the property’s location, design, setting, materials,
workmanship, feeling, or association.38 The regulations further clarify that both direct and indirect
effects of the project must be considered, as well as reasonably foreseeable effects that may occur
later in time, may occur at some distance, or are cumulative.39 If an agency, through consultation
with the SHPO/THPO, determines the potential undertaking may result in adverse effects to a
historic property (or properties), the agency issues a finding to that effect and formally notifies
the ACHP. The agency then proceeds to “Step 4: Resolution.”40
If the agency finds that the undertaking will not adversely affect any historic properties, it issues a
proposed finding of “no adverse effect.” Regulations require the agency to document its finding
to the SHPO/THPO, notify all consulting parties, and provide information on the finding to the

36 For example, routine repainting of a historic structure may have an effect on the historic property, but that effect
usually is not considered adverse under Section 106.
37 36 C.F.R. §800.5(a)(1).
38 Ibid.
39 Ibid.
40 Notification of an adverse effect finding is a procedural requirement under Section 106. Failure to notify the ACHP
and provide it with the opportunity to join the resolution process under 36 C.F.R. §800.6 could result in the ACHP
finding invalid any memorandum of agreement (MOA) entered into.
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public on request.41 If the SHPO/THPO does not comment within 30 days, the agency’s
responsibilities under Section 106 are fulfilled.42
Does a Consulting Party Disagree with the Agency’s Finding of No Adverse
Effects?
During the review period, a consulting party or the ACHP may disagree with or dispute an
agency’s finding of no adverse effects. If a consulting party objects to such a finding, the agency
has two options: (1) continue consultation with the SHPO/THPO or other relevant parties or (2)
submit the finding directly to the ACHP for an opinion.43 For an overview of how agencies and
consulting parties address disagreements, see the Appendix.
If the agency—through consultation with the SHPO/THPO or following an opinion from the
ACHP—reverses an initial finding of no adverse impacts, the agency then proceeds to “Step 4:
Resolution.”
Step 4: Resolution
In the final step of the Section 106 process, the agency explores measures to avoid, minimize, or
mitigate any adverse effects on historic properties. Through this process, agencies work to reach
agreement with the consulting parties (and, in some cases, the ACHP) on measures to address
such adverse effects (see Figure 4). Whereas regulations are clear about the process agencies
must adhere to under Section 106, there are few requirements as to what measures may be
considered or agreed to through such agreements. Instead, various solutions are usually available
for consideration by consulting parties and the agency, and the ACHP often encourages creative
or innovative mitigation measures.44

41 36 C.F.R. §800.5(c). Regulations at 36 C.F.R. 800.11(e) establish the documentation requirements for an agency
when issuing a finding for review at this stage. The requirements include an explanation of why the agency found the
criteria of adverse effect applicable or inapplicable, including any conditions or future actions to avoid, minimize, or
mitigate adverse effects.
42 36 C.F.R. §800.5(c)(1).
43 36 C.F.R. §800.5(c)(2).
44 ACHP, “Guidance on Agreement Documents,” at https://www.achp.gov/initiatives/guidance-agreement-documents.
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Effects on National Historic Landmarks
The National Historic Landmarks (NHL) program—like the National Register of Historic Places—is a federal
recognition program administered by the National Park Service (NPS). Whereas National Register properties are
considered historic primarily due to their state and/or local significance, NHLs are considered places of national
significance to the history of the United States. As of 2023, there were more than 2,600 NHLs located across the
country (compared with nearly 100,000 properties listed on the National Register).
For undertakings with the potential to affect properties designated as NHLs, federal agencies are required to
fol ow the Section 106 process established for other historic properties. However, when considering measures to
avoid, minimize, or mitigate potential adverse effects, the National Historic Preservation Act (NHPA) establishes a
higher standard of protection for NHLs than for other historic properties. Whereas the NHPA only requires
agencies to “take into account” an undertaking’s effect on a historic property, Section 110 of the NHPA requires
agencies, “to the maximum extent possible, [to] undertake such planning and actions as may be necessary to
minimize harm” to an NHL (54 U.S.C. §306107). Additionally, when adverse effects to an NHL are found, the
agency is required to request the participation of the Advisory Council on Historic Preservation and the Secretary
of the Interior in the consultation process (36 C.F.R. §§800.10(b)-(c)).
Source: 36 C.F.R. §800.10.
Figure 4. Resolution

Source: CRS, using 36 C.F.R. §800.5 and 36 C.F.R. §800.6.
Do the Agency and Consulting Parties Agree on How to Address Potential
Adverse Effects?
If an agency determines a proposed undertaking may result in adverse effects to one or more
historic properties, the agency is directed to consult with the SHPO/THPO, the ACHP, and/or
other relevant consulting parties to reach a formal agreement as to how to proceed with the
undertaking. If the relevant parties agree on a solution, they are directed to enter into a legally
binding agreement known as a memorandum of agreement (MOA).45 The MOA “govern[s] the

45 Regulations allow agencies to enter into types of agreements other than an MOA. For example, programmatic/project
agreements are often used for large, complex projects or projects wherein the agency cannot fully determine how a
particular undertaking may affect historic properties due to the scale of the project. In addition, agencies may
incorporate measures to avoid, minimize, or mitigate adverse effects to historic properties in a record of decision,
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undertaking and all of its parts,” including how the agency plans to address adverse effects.46 In
general, MOAs contain information detailing each of the avoidance, minimization, or mitigation
measures the federal agency has agreed to implement, as well as provisions outlining what
happens when the expected effects from the undertaking change or when the undertaking is
modified, when disputes arise, and when new historic properties are discovered. The agency
provides the MOA and associated documentation to the ACHP.47
What Happens If the Parties Do Not Enter into an Agreement?
According to the ACHP, the “vast majority” of federal undertakings that affect a historic property
are resolved through an MOA or other agreement between the agency and the consulting parties.48
In the instances where the parties are unable to reach agreement, the alternative is terminating
consultation. Failure to reach an agreement may occur for any number of reasons. For example,
an agency may determine—despite the objections of the SHPO/THPO, ACHP, or other consulting
parties—that the nature of a specific undertaking makes avoidance of potential adverse effects
impossible or impractical. This could be due to the scale of the undertaking, its proximity to the
historic property, or technical constraints that may not, in the agency’s view, allow for direct
mitigation or avoidance measures. Alternatively, failure to reach an agreement could result from
disagreement on whether particular mitigation or avoidance measures are appropriate and/or
sufficient. Regardless of the scenario, any party, including the agency, the SHPO/THPO, or the
ACHP, may terminate consultation.49
If any party other than the agency (e.g., SHPO/THPO, certain consulting parties, ACHP)
terminates consultation, the agency is authorized to enter into an agreement with any remaining
consulting parties, if appropriate. If the agency ends the consultation process, it must make its
termination decision and supporting documents available to the public and all consulting parties.50
The agency also must submit its findings for termination to the ACHP for comment. The ACHP
has 45 days to respond to the decision; however, the agency is not required to revise its initial
decision based on ACHP comments. Instead, the agency is required to “take into account the
Council’s comments in reaching a final decision on the undertaking.”51 If the agency’s final
decision affirms the initial finding, the agency is required to formally document that decision and
provide evidence of consideration of the ACHP opinion (see Appendix). Once this
documentation is complete, the agency has fulfilled its Section 106 requirements.

which is established through the NEPA process.
46 36 C.F.R. §800.6(c)(1).
47 36 C.F.R. §800.6(b)(1)(iv).
48 ACHP, “Guidance on Agreement Documents: Failure to Agree,” at https://www.achp.gov/failure_to_agree. Other
agreements could include a programmatic agreement (see “Section 106 Program Alternatives” text box), which may be
appropriate in certain situations (e.g., multiple or complex undertakings where effects to historic properties may not be
fully determined in advance).
49 36 C.F.R. §800.7(a).
50 36 C.F.R. §800.7(c)(4).
51 36 C.F.R. §800.7(c)(4).
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Appendix. Dispute Process
At various points throughout the Section 106 process, consulting parties may disagree with an
agency’s finding or determination. Regulations require the agency to issue formal findings at two
separate stages: (1) findings of no historic properties within a project’s area of potential effects or
(2) findings of no adverse effects on historic properties. In both instances, regulations provide a
process and timeline for how to resolve or document consulting parties’ objections to these
findings.
In general, the state or tribal historic preservation officer (SHPO/THPO) must respond within 30
days of receiving an agency finding or determination. If the SHPO/THPO does not comment
within 30 days, the agency’s responsibilities under Section 106 are fulfilled and the undertaking
may proceed. If the SHPO/THPO objects to the agency finding within the 30-day window, the
agency has two options: (1) continue consultation with the SHPO/THPO or other relevant parties
or (2) submit findings directly to the ACHP for an opinion.
Figure A-1. Section 106 Dispute Process

Source: Congressional Research Service. For disagreements regarding a finding of no historic properties, see 36
C.F.R. §800.4(d); for findings of no adverse effects, see 36 C.F.R. §800.5(c); for the documentation process in the
event of a failure to reach an agreement, see 36 C.F.R. §800.7; for general documentation requirements, see 36
C.F.R. §800.11.
Note: ACHP = Advisory Council on Historic Preservation.
If the agency opts to forgo further consultation and involve the ACHP, the ACHP has 30 days to
issue an opinion on the agency’s finding at its discretion.52 The ACHP’s opinion is not binding on

52 36 C.F.R. §800.4(d)(1)(iv). The timeline for ACHP response may differ for an opinion on an agency’s finding of no
adverse impacts. Regulations in this scenario specify that the ACHP has 15 days to issue an opinion at its discretion,
although regulations permit an extension of an addition 15 days, if needed (36 C.F.R. §800.5(c)(3)).
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the agency; however, the agency must “take into account the Council’s opinion in reaching a final
decision on the finding.”53 If the ACHP does not respond within 30 days of receiving the request,
the agency’s responsibilities under Section 106 are fulfilled.
If the agency—through further consultation with the SHPO/THPO or following an opinion from
the ACHP—reverses its initial finding, the agency proceeds with the Section 106 process. If the
final decision of the agency affirms the initial finding, the agency is required to prepare a
summary of the decision that documents the agency’s rationale for the decision and evidence of
consideration of the ACHP opinion. This summary is provided to the ACHP, the SHPO/THPO,
and the consulting parties and is made available to the public. At this point, the agency has
fulfilled its requirements under Section 106.

Author Information

Mark K. DeSantis

Analyst in Natural Resources Policy

Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan
shared staff to congressional committees and Members of Congress. It operates solely at the behest of and
under the direction of Congress. Information in a CRS Report should not be relied upon for purposes other
than public understanding of information that has been provided by CRS to Members of Congress in
connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not
subject to copyright protection in the United States. Any CRS Report may be reproduced and distributed in
its entirety without permission from CRS. However, as a CRS Report may include copyrighted images or
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copy or otherwise use copyrighted material.

53 36 C.F.R. §800.5(c)(3)(ii)(A).
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