Order Code RL32528
CRS Report for Congress
Received through the CRS Web
International Law and Agreements:
Their Effect Upon U.S. Law
August 16, 2004
Michael Garcia
Legislative Attorney
American Law Division
Arthur Traldi
Law Clerk
American Law Division
Congressional Research Service ˜ The Library of Congress

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International Law and Agreements: Their Effect Upon
U.S. Law
Summary
This report provides an introduction as to the roles that international law and
agreements play in the United States. International law is derived from two primary
sources — international agreement and customary practice. Under the U.S. legal
system, international agreements can be entered into either pursuant to a treaty or via
executive agreement. The United States Constitution allocates primary responsibility
for entering such agreements to the Executive branch, but Congress also plays an
essential role. First, in order for a treaty (but not an executive agreement) to become
binding upon the United States, the Senate must provide its advice and consent to
treaty ratification by a two-thirds majority. Secondly, Congress may authorize
congressional-executive agreements. Thirdly, many treaties and executive agreements
are not self-executing, meaning that in order to take effect domestically,
implementing legislation is required to provide U.S. bodies with the authority
necessary to enforce and comply with an international agreement’s provisions.
The status of an international agreement within the United States is dependant
upon a variety of factors. Self-executing treaties have a status equal to federal
statute, superior to state law, and inferior to the Constitution. Depending upon the
nature of executive agreements, they may or may not have a status equal to federal
statute. In any case, self-executing executive agreements have a status that is
superior to state law and inferior to the Constitution. Treaties or executive
agreements which are not self-executing have been understood by the courts to have
limited status domestically; rather, the legislation or regulations implementing these
agreements are controlling domestically.
The effects of the second source of international law, customary international
practice, upon the United States are more ambiguous and controversial. While there
is some Supreme Court jurisprudence finding that customary international law is part
of U.S. law, conflicting U.S. statutes remain controlling. Customary international
law is most clearly recognized under U.S. law via the Alien Tort Claims Act
(ATCA), which establishes federal court jurisdiction over tort claims brought by
aliens for violations of “the law of nations.” The scope of this statute was recently
clarified by the Supreme Court in Sosa v. Alvarez-Machain.
Recently, there has been some controversy concerning references made by U.S.
courts to foreign laws or jurisprudence when interpreting domestic statutes.
Historically, U.S. courts have on occasion looked to foreign jurisprudence for
persuasive value, but foreign jurisprudence never appears to have been thought of as
binding. Though U.S. courts will likely continue to refer to foreign jurisprudence,
where, when, and how significantly they will rely upon it is difficult to predict.

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Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Forms of International Agreements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Treaties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Executive Agreements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Effects of International Agreements on U.S. Law . . . . . . . . . . . . . . . . . . . . . 5
Self-Executing vs. Non-Self-Executing Agreements . . . . . . . . . . . . . . . 5
Conflict of Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Customary International Law . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
The Alien Tort Claims Act . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Reference to Foreign Law by U.S. Courts . . . . . . . . . . . . . . . . . . . . . . . . . . 11

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International Law and Agreements: Their
Effect Upon U.S. Law
Introduction
International law consists of “rules and principles of general application dealing
with the conduct of states and of international organizations and with their relations
inter se, as well as with some of their relations with persons, whether natural or
juridical.”1 Rules of international law can be established in three main ways: (1) by
international, formal agreement, usually between States, (2) in the form of
international custom, and (3) by derivation of principles common to major world
legal systems (hereinafter referred to as foreign law).2
Since its inception, the United States has understood international legal
commitments to be binding upon it both internationally and domestically.3 The
1 RESTATEMENT (THIRD) OF FOREIGN RELATIONS, § 101 (1987). Recorded international law
dates back to agreements between Mesopotamian rulers five thousand years ago, but
international law as we understand it began with the Roman Empire, whose scholars
formulated a jus gentium (law of nations) they believed universally derivable through
reason. See generally DAVID J. BEDERMAN, INTERNATIONAL LAW IN ANTIQUITY (2001).
The term “international law” was coined by Jeremy Bentham in 1789. JEREMY BENTHAM,
AN INTRODUCTION TO THE PRINCIPLES OF MORALS AND LEGISLATION 326 n. 1 (Hafner
Publ’g Co. 1948) (1789). Although originally governing State-to-State relations, the scope
of international law has grown, beginning in the latter half of the 20th century with the
emerging fields of human rights law and international criminal law, to regulate the treatment
and conduct of individuals in certain circumstances. See, e.g., Universal Declaration on
Human Rights, UN GAOR, Supp. No. 16, UN Doc. A/6316 (1948); Geneva Convention
(Third) Relative to the Treatment of Prisoners of War, Aug. 12, 1949, 6 U.S.T. 3316, 75
U.N.T.S. 135; Geneva Convention (Fourth) Relative to the Protection of Civilian Persons
in Times of War, Aug. 12, 1949, 6 U.S.T. 3516, 75 U.N.T.S. 287; International Covenant
on Civil and Political Rights, G.A. Res. 2200A, U.N. GAOR, 3rd Comm., 21st Sess., 1496th
plen. mtg., U.N. Doc. A/RES/2200A (XXI) (1966). See also U.S. STATE DEPT. PUB. NO.
3080, REPORT OF ROBERT H. JACKSON, INTERNATIONAL CONFERENCE ON MILITARY TRIALS
437 (1949) (arguing that crimes against humanity were “implicitly” in violation of
international law even before Nuremberg).
2 RESTATEMENT, supra note 1, § 102.
3 See, e.g., Ware v. Hylton, 3 U.S. (3 Dall.) 199, 281 (1796) (“[w]hen the United States
declared their independence, they were bound to receive the law of nations, in its modern
state of purity and refinement”); Chisholm v. Georgia, 2 U.S. (2 Dall.) 419 (1793) (“the
United States had, by taking a place among the nations of the earth, become amenable to the
law of nations”); see also Letter from Thomas Jefferson, Secretary of State, to M. Genet,
French Minister (June 5, 1793) (construing the law of nations as an “integral part” of
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United States assumes international obligations most frequently when it makes
agreements with other States or international bodies that are intended to be legally
binding upon the parties involved. Such legal agreements are made through treaty
or executive agreement. The United States Constitution allocates primary
responsibility for such agreements to the Executive, but Congress also plays an
essential role. First, in order for a treaty (but not an executive agreement) to become
binding upon the United States, the Senate must provide its advice and consent to
treaty ratification by a two-thirds majority.4 Secondly, Congress may authorize
congressional-executive agreements. Thirdly, in order to take effect domestically,
many treaties and executive agreements require implementing legislation that
provides U.S. bodies with the authority necessary to enforce and comply with an
international agreement’s provisions.5
The effects of customary international law and foreign law upon the United
States are more ambiguous and controversial. There is some Supreme Court
jurisprudence finding that customary international law is incorporated into domestic
law, but this incorporation is only to the extent that “there is no treaty, and no
controlling executive or legislative act or judicial decision” in conflict.6 Though
foreign law has long been seen as persuasive by American courts, its recent use in
certain regards (particularly with respect to interpreting the Constitution) has
prompted some criticism by a number of law-makers and scholars. This report
provides an introduction to the role that international law and agreements play in the
United States.
3 (...continued)
domestic law).
4 U.S. CONST. art. II, § 2 (providing that the President “shall have Power, by and with the
Advice and Consent of the Senate, to make Treaties, provided two-thirds of the Senators
present concur”).
5 See, e.g., Foster v. Neilson, 27 U.S. (2 Pet.) 253, 314 (1828) (Marshall, J.) (finding that
international agreements entered into by the United States are “to be regarded in courts of
justice as equivalent to an act of the legislature, wherever it operates of itself, without the
aid of any legislative provision. But when the terms of the stipulation import a contract,
when either of the parties engages to perform a particular act, the [agreement] addresses
itself to the political, not the judicial department; and the legislature must execute the
contract, before it can become a rule for the court”). CONGRESSIONAL RESEARCH SERVICE,
TREATIES AND OTHER INTERNATIONAL AGREEMENTS: THE ROLE OF THE UNITED STATES
SENATE, A STUDY PREPARED FOR THE SENATE COMM. ON FOREIGN RELATIONS 4 (Comm.
Print 2001); RESTATEMENT, supra note 1, § 111(3).
6 The Paquete Habana, 175 U.S. 677, 700 (1900). See also, e.g., United States v. Yousef,
327 F.3d 56 (2nd Cir. 2003); Galo-Garcia v. I.N.S., 86 F.3d 916 (9th Cir. 1996) (“where a
controlling executive or legislative act...exist[s], customary international law is
inapplicable”); Committee of U.S. Citizens Living in Nicaragua v. Reagan, 859 F.2d 929,
939 (D.C. Cir.1988); Garcia-Mir v. Meese, 788 F.2d 1446, 1453 (11th Cir.), cert. denied, 479
U.S. 889 (1986). But see Sosa v. Alvarez-Machain, 124 S.Ct. 2739 (U.S. 2004) (holding
that the Alien Tort Claims Act, 28 U.S.C.A. § 1350, recognized an individual cause of
action for some egregious violations of the law of nations).

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Forms of International Agreements
As previously mentioned, the United States regularly enters into international
agreements with other States or international organizations that are legally binding.
This section briefly describes the form that these agreements may take under
domestic practice. In this regard, it is important to distinguish “treaty” in the context
of international law, in which “treaty” and “international agreement” are synonymous
terms for all binding agreements,7 and “treaty” in the context of domestic American
law, in which “treaty” more narrowly refers to a particular subcategory of binding
international agreements.

Treaties. Under U.S. law, a treaty is an agreement negotiated and signed8 by
the Executive branch that enters into force if it is approved by a two-thirds majority
of the Senate and is subsequently ratified by the President. In some cases, such as in
many bilateral treaties, ratification occurs through Presidential signature. In the case
of certain multilateral treaties, ratification may occur only after the treaty’s
instruments of ratification are submitted to the appropriate body in accordance with
the terms of the agreement.
The Senate may, in considering a treaty, condition its consent on certain
reservations,9 declarations10 and understandings11 concerning treaty application. If
accepted, these reservations, declarations, and understandings may limit and/or define
U.S. obligations under the treaty.12
7 Vienna Convention on the Law of Treaties, entered into force Jan. 27, 1980, 1155 U.N.T.S.
331 [hereinafter “Vienna Convention”], art.2. Although the United States has not ratified
the Vienna Convention, it recognizes it as generally signifying customary international law.
See, e.g., Fujitsu Ltd. v. Federal Exp. Corp., 247 F.3d 423 (2nd Cir. 2001) (“we rely upon the
Vienna Convention here as an authoritative guide to the customary international law of
treaties...[b]ecause the United States recognizes the Vienna Convention as a codification of
customary international law...and [it] acknowledges the Vienna Convention as, in large part,
the authoritative guide to current treaty law and practice”) (internal citations omitted).
8 Under international law, States that have signed but not ratified treaties have the obligation
to refrain from acts that would defeat the object or purpose of the treaty. See Vienna
Convention, art. 18.
9 A “reservation” is “a unilateral statement... made by a State, when signing, ratifying,
accepting, approving or acceding to a treaty, whereby it purports to exclude or to modify the
legal effect of certain provisions of the treaty in their application to that State.” Id.
art.2(1)(d). In practice, “[r]eservations change U.S. obligations without necessarily
changing the text, and they require the acceptance of the other party.” TREATIES AND OTHER
INTERNATIONAL AGREEMENTS, supra note 5, at 11; Vienna Convention, arts. 19-23.
10 Declarations are “statements expressing the Senate’s position or opinion on matters
relating to issues raised by the treaty rather than to specific provisions.” TREATIES AND
OTHER INTERNATIONAL AGREEMENTS, supra note 5, at 11.
11 Understandings are “interpretive statements that clarify or elaborate provisions but do not
alter them.” Id.
12 As a matter of customary international law, States are “obliged to refrain from acts which
would defeat the object and purpose of a treaty,” including entering reservations that are
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Executive Agreements. The great majority of international agreements that
the United States enters into are not treaties but executive agreements13 —
agreements entered into by the Executive branch that are not submitted to the Senate
for its advice and consent. Congress generally requires notification upon the entry
of such an agreement.14 There are three types of prima facie legal executive
agreements: (1) congressional-executive agreements, in which Congress has
previously or retroactively authorized an international agreement entered into by the
Executive; (2) executive agreements made pursuant to an earlier treaty, in which the
agreement is authorized by a ratified treaty; and (3) sole executive agreements, in
which an agreement is made pursuant to the President’s constitutional authority
without further congressional authorization. The Executive’s authority to promulgate
the agreement is different in each case.
In the case of congressional-executive agreements, the “constitutionality...seems
well established.”15 Unlike in the case of treaties, where only the Senate plays a role in
authorizing the agreement, both houses of Congress will be involved in the authorizing
process for congressional-executive agreements. Congressional authorization of such
agreements takes the form of a statute which must pass both houses of Congress.
Historically, congressional-executive agreements have been made for a wide variety
of topics, ranging from postal conventions to bilateral trade to military assistance.16
The North American Free Trade Agreement and the General Agreement on Tariffs and
Trade are notable examples of congressional-executive agreements.
Agreements made pursuant to treaties are also well-established as legitimate,
though controversy occasionally arises as to whether the agreement was actually
imputed by the treaty in question.17 Since the earlier treaty is the “Law of the Land,”18
the power to enter into an agreement required or contemplated by the treaty lies fairly
clearly within the President’s executive function.
Sole executive agreements rely on neither treaty nor congressional authority to
provide for their legal basis. There are a number of provisions in the Constitution that
may confer limited authority upon the President to promulgate such agreements on the
12 (...continued)
incompatible with a treaty’s purposes. Vienna Convention, arts. 18-19.
13 LOUIS HENKIN, FOREIGN AFFAIRS AND THE U.S. CONSTITUTION 215 (2nd ed. 1996).
14 See 1 U.S.C. § 112b (requiring text of executive agreements to be transmitted to Congress
within 60 days, subject to certain exceptions).
15 TREATIES AND OTHER INTERNATIONAL AGREEMENTS, supra note 5, at 5. See also CRS
Report 97-896, Why Certain Trade Agreements Are Approved as Congressional-Executive
Agreements Rather than as Treaties; HENKIN, supra note 13, at 215-18.
16 TREATIES AND OTHER INTERNATIONAL AGREEMENTS, supra note 5, at 5.
17 Id.
18 U.S. CONST. art. VI, § 2 (“the laws of the United States...[and] all treaties made, or which
shall be made, under the authority of the United States, shall be the supreme Law of the
Land”).

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basis of his foreign affairs power.19 If the President enters into an executive agreement
pursuant to and dealing with an area where he has clear, exclusive constitutional
authority — such as an agreement to recognize a particular State for diplomatic
purposes — the agreement is legally permissible regardless of Congress’s opinion on
the matter.20 If, however, the President enters into an agreement and his constitutional
authority over the agreement’s subject matter is unclear, a reviewing court may
consider Congress’s position in determining whether the agreement is legitimate.21 If
Congress has given its implicit approval to the President entering the agreement, or is
silent on the matter, it is more likely that the agreement will be deemed valid. When
Congress opposes the agreement and the President’s constitutional authority to enter
the agreement is ambiguous, it is unclear if or when such an agreement would be given
effect. The Atlantic Charter, which President Franklin Roosevelt and British Prime
Minister Winston Churchill agreed to in 1941 to delineate Anglo-American war aims,
is an example of a sole executive agreement.
Effects of International Agreements on U.S. Law
The effects that international agreements entered into by the United States have
upon U.S. domestic law are dependent upon the nature of the agreement — whether the
agreement is self-executing or non-self-executing, and possibly whether it was made
pursuant to a treaty or an executive agreement.
Self-Executing vs. Non-Self-Executing Agreements. Certain
international treaties or executive agreements are considered “self-executing,” meaning
that they have the force of law without the need for subsequent congressional action.
However, many other treaties and agreements are not considered self-executing, and
are understood to require implementing legislation to take effect, as enforcing U.S.
agencies otherwise lack authority to conduct the actions required to ensure compliance
with the international agreement.22 Treaties have been found to be non-self-executing
for at least three reasons: (1) the agreement manifests an intention that it shall not
become effective as domestic law without the enactment of implementing legislation,
(2) the Senate in giving consent to a treaty, or Congress by resolution, requires
19 See TREATIES AND OTHER INTERNATIONAL AGREEMENTS, supra note 5, at 5, citing U.S.
CONST. arts. II, § 1 (executive power), § 2 (commander in chief power, treaty power), § 3
(receiving ambassadors). Courts have recognized foreign affairs as an area of very strong
executive authority. See United States v. Curtiss-Wright Export Corp., 299 U.S. 304 (1936).
20 See RESTATEMENT, supra note 1, § 303 (4).
21 See Dames & Moore v. Regan, 453 U.S. 654 (1981) (establishing that Congress’s implicit
approval of Executive action, such as a historical practice of yielding authority in a
particular area, may legitimize an agreement); Youngstown Sheet & Tube Co. v. Sawyer,
343 U.S. 579 (1952) (“When the President acts pursuant to an express or implied
authorization of Congress, his powers are at their maximum.... Congressional inertia,
indifference or quiescence may... invite, measures of independent Presidential
responsibility.... When the President takes measures incompatible with the expressed or
implied will of Congress, his power is at its lowest ebb, for then he can rely only upon his
own constitutional powers minus any constitutional powers of Congress over the matter”)
(Jackson, J., concurring).
22 See generally RESTATEMENT, supra note 1, § 111(4)(a) & cmt. h.

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implementing legislation,23 or (3) implementing legislation is constitutionally
required.24 There is significant scholarly debate regarding the distinction between self-
executing and non-self-executing agreements, including the ability of U.S. courts to
apply and enforce them.25
Until implementing legislation is enacted, existing domestic law concerning
amatter covered by an international agreement that is not self-executing remains
unchanged and controlling law in the United States. However, when a treaty is
ratified or an executive agreement is entered, the United States acquires
obligations under international law and may be in default of those obligations
unless implementing legislation is enacted.26
Conflict of Laws. Sometimes, a treaty or executive agreement will conflict
with one of the three main tiers of domestic law — state law, federal law, or the
Constitution. For domestic purposes, a ratified, self-executing treaty is the law of the
land equal to federal law27 and superior to state law,28 but inferior to the Constitution.29
A self-executing executive agreement is likely superior to state law,30 but sole
executive agreements may be inferior to conflicting federal law in certain
circumstances (congressional — executive agreements or executive agreements
pursuant to treaties are equivalent to federal law),31 and all executive agreements are
23 For example, in the case of the United Nations Convention Against Torture and Other
Cruel, Inhuman or Degrading Treatment or Punishment, G.A. Res. 39/46, Annex, 39 U.N.
GAOR Supp. No. 51, U.N. Doc. A/39/51 (1984), the Senate gave advice and consent subject
to a declaration that the treaty was not self-executing. U.S. Reservations, Declarations, and
Understandings to the Convention Against Torture and Other Cruel, Inhuman or Degrading
Treatment or Punishment, 136 CONG. REC. S17486-01 (daily ed., Oct. 27, 1990).
24 RESTATEMENT, supra note 1, § 111(4)(a) & reporters’ n. 5-6.
25 See, e.g., John H. Jackson, Status of Treaties in Domestic Legal Systems: A Policy
Analysis, 86 AM. J. INT’L L. 310 (1992); Jordan J. Paust, Self-Executing Treaties, 82 AM.
J. INT’L L. 760 (1988); Carlos Manuel Vázquez, The Four Doctrines of Self-Executing
Treaties, 89 AM. J. INT’L L. 695 (1995); John C. Yoo, Globalism and the Constitution:
Treaties, Non-Self-Execution, and the Original Understanding, 99 COLUM. L. REV. 1955
(1999).
26 See RESTATEMENT, supra note 1, § 111, cmt. h.
27 See Whitney v. Robertson, 124 U.S. 190 (1888).
28 See Ware v. Hylton, 3 U.S. (3 Dall.) 199 (1796).
29 See Reid v. Covert, 354 U.S. 1 (1957); Doe v. Braden, 57 U.S. 635, 657 (1853) ( “[t]he
treaty is therefore a law made by the proper authority, and the courts of justice have no right
to annul or disregard any of its provisions, unless they violate the Constitution of the United
States”). See generally RESTATEMENT, supra note 1, § 115.
30 United States v. Belmont, 301 U.S. 324 (1937); United States v. Pink, 315 U.S. 203.
(1942).
31 Executive agreements have been held to be inferior to conflicting federal law when the
agreement concerns matters expressly within the constitutional authority of Congress. See,
e.g., United States v. Guy W. Capps, Inc., 204 F.2d 655 (4th Cir. 1953) (finding that
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inferior to the Constitution.32 In cases where ratified treaties or certain executive
agreements are equivalent to federal law, the “last in time” rule establishes that a more
recent statute will trump an earlier, inconsistent international agreement, while a more
recent self-executing agreement will trump an earlier, inconsistent statute.33 In the case
of treaties and executive agreements that are not self-executing, it is the implementing
legislation that is controlling domestically, not the agreements or treaties themselves.34
Customary International Law
Customary international law is defined as resulting from “a general and consistent
practice of States followed by them from a sense of legal obligation.”35 This means
that all, or nearly all, States consistently follow the practice in question and they must
do so because they believe themselves legally bound, a concept often referred to as
opinio juris sive necitatis (opinio juris). If States generally follow a particular practice
but do not feel bound by it, it does not constitute customary international law.36
Further, there are ways for States to avoid being subject to customary international law.
First, a State which is a persistent objector to a particular requirement of customary
31 (...continued)
executive agreement contravening provisions of import statute was unenforceable);
RESTATEMENT, supra note 1, § 115 reporters’ n.5. However, an executive agreement may
trump pre-existing federal law if it concerns an enumerated or inherent Executive power
under the Constitution, or if Congress has historically acquiesced to the President entering
agreements in the relevant area. See Pink, 315 U.S. at 230 (“[a]ll Constitutional acts of
power, whether in the executive or in the judicial department, have as much legal validity
and obligation as if they proceeded from the legislature”) (quoting THE FEDERALIST NO. 64
(John Jay)); Dames & Moore, 453 U.S. at 654 (upholding sole executive agreement
concerning the handling of Iranian assets in the United States, despite the existence of a
potentially conflicting statute, given Congress’s historical acquiescence to these types of
agreements).
32 See generally RESTATEMENT, supra note 1, § 115.
33 Whitney v. Robertson, 124 U.S. 190 (1888).
34 Congress may enact legislation in order to comply with U.S. treaty obligations that would
otherwise intrude upon a state’s traditional rights under the 10th Amendment. In the 1920
case of Missouri v. Holland, 252 U.S. 416 (1920), the Supreme Court upheld a federal law
regulating the killing of migratory birds that had been adopted pursuant to a treaty between
the United States and Great Britain, notwithstanding the fact that a similar statute enacted
in the absence of a treaty had been ruled unconstitutional on 10th Amendment grounds. The
extent to which Congress may intrude upon traditional state authority through treaty-
implementing legislation remains unclear, though there is reason to believe that it could not
enact legislation that infringed upon the essential character of states, such as through
legislation that commandeered state executive and legislative authorities. See Printz v.
United States, 521 U.S. 898 (1997); New York v. United States, 505 U.S. 144 (1992); see
generally Edward T. Swaine, Does Federalism Constrain the Treaty Power?, 103 COLUM.
L. REV. 403 (2003).
35 RESTATEMENT, supra note 1, § 102(2).
36 Id. § 102 cmt. c.

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international law is exempt from it.37 Second, under American law, the United States
can exempt itself from customary international law requirements by passing a
contradictory statute under the “last in time” rule.38 As a result, while customary
international law may be incorporated, its impact when in conflict with other domestic
law appears limited.
In examining State behavior to determine whether opinio juris is present, courts
might look to a variety of sources, including, inter alia, relevant treaties, unanimous
or near-unanimous declarations by the United Nations General Assembly concerning
international law,39 and whether noncompliance with an espoused universal rule is
treated as a breach of that rule.40
In 1900, the Supreme Court stated that customary international law “is our law,”
but only when there is not already a controlling executive or legislative act.41 There
does not appear to be a case where the Court has ever struck down a U.S. statute on the
ground that it violated customary international law. However, customary international
law can potentially affect how domestic law is construed. If two constructions of an
ambiguous statute are possible, one of which is consistent with international legal
obligations and one of which is not, courts will often construe the statute so as not to
violate international law, presuming such a statutory reading is reasonable.42
37 Id. § 102, reporters’ n. 2. The philosophy underlying the consistent objector exemption
is that States are bound by customary international law because they have at least tacitly
consented to it. Binding them to abide to customary practices despite their explicit rejection
of these norms would violate their sovereign rights — though States are likely still bound
in the case of peremptory, jus cogens norms which are thought to permit no State
derogation, such as the international prohibition against genocide or slavery. See Colom v.
Peru, 1950 I.C.J. 266 (Nov. 20); U.K. v. Norway, 1951 I.C.J. 116 (Dec.18). For a discussion
of one instance of the consistent objector rule, see Curtis A. Bradley, The Juvenile Death
Penalty and International Law, 52 DUKE L.J. 485 (2002). See also Stanford v. Kentucky,
492 U.S. 361 (1989) (allowing the death penalty for sixteen year olds despite international
norms to the contrary).
38 Whitney v. Robertson, 124 U.S. 190 (1888).
39 RESTATEMENT, supra note 1, § 102 (2) cmt. c. For a discussion of potential difficulties in
relying U.N. General Assembly Resolutions as evidence of customary international law, see
Oscar Schachter, International Law in Theory and Practice: General Course in Public
International Law, 178 REC. DES COURS 111-121 (1982-V).
40 See Sosa v. Alvarez-Machain, 124 S.Ct. 2739, 2767 (2004) (declining to apply protections
espoused by the Universal Declaration of Human Rights because it “does not of its own
force impose obligations as a matter of international law”).
41 The Paquete Habana, 175 U.S. at 700. As a result, it is the opinion of some commentators
that “no enactment of Congress may be challenged on the grounds that it violates customary
international law.” Wade Estey, The Five Bases of Extraterritorial Jurisdiction and the
Failure of the Presumption Against Extraterritoriality, 21 HASTINGS INT’L. & COMP. L.
REV. 177, 180 (1997). See also Committee of U.S. Citizens Living in Nicaragua, 859 F.2d
at 940.
42 Murray v. Schooner Charming Betsy, 6 U.S. (2 Cranch) 64, 118 (1804) (Marshall, J.) (“an
act of Congress ought never to be construed to violate the law of nations if any other
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Some particularly prevalent rules of customary international law can acquire the
status of jus cogens norms — peremptory rules which permit no derogation, such as
the international prohibition against slavery or genocide.43 For a particular area of
customary international law to constitute a jus cogens norm, State practice must be
extensive and virtually uniform.44
The Alien Tort Claims Act. Perhaps the clearest example of U.S. law
incorporating customary international law is via the Alien Tort Claims Act (ATCA).45
The ATCA originated as part of the Judiciary Act of 1789, and establishes federal court
jurisdiction over tort claims brought by aliens for violations of “the law of nations.”46
Until 1980, this statute was rarely used, but in Filartiga v. Pena-Irala, the Second
Circuit relied upon it to award a civil judgment against a former Paraguayan police
official who had allegedly tortured the plaintiffs while still in Paraguay. In doing so,
the Filartiga Court concluded that torture constitutes a violation of the law of nations
and gives rise to a cognizable claim under the ATCA.47 Since that time, the ATCA has
been used by aliens on a number of occasions to pursue civil judgments against persons
or entities for alleged human rights violations.48
Until recently the Supreme Court had not addressed the scope of the causes of
action available to aliens under the ATCA. In 2004, however, the Supreme Court
heard Sosa v. Alvarez-Machain,49 a case in which the plaintiff attempted to derive from
the Alien Tort Claims Act a cause of action for violation of rules of customary
42 (...continued)
possible construction remains....”). But see Sampson v. Federal Republic of Germany, 250
F.3d 1145, 1151-54 (7th Cir. 2001) (suggesting that given the “present uncertainty about the
precise domestic role of customary international law,” application of this canon of
construction to resolve differences between ambiguous congressional statutes and customary
international law should be used sparingly).
43 RESTATEMENT, supra note 1, § 702, cmt. n.
44 Buell v. Mitchell, 274 F.3d 337 (6th Cir. 2001), citing North Sea Continental Shelf
(Federal Republic of Germany/Denmark; Federal Republic of Germany/The Netherlands)
1969 I.C.J. 51/52 (Feb. 20) & RESTATEMENT, supra note 1, § 102 (2) cmt. k. & reporters’
n. 6.
45 28 U.S.C. § 1350.
46 For additional background on the ATCA, see CRS Report RL32118, The Alien Tort
Statute: Legislative History and Executive Branch Views.
47 630 F.2d 876 (2nd Cir. 1980). The court based its conclusion that torture was prohibited
under international law upon sources including, inter alia, U.N. resolutions, the U.N.
Charter, and the Universal Declaration of Human Rights.
48 See, eg., Flores v. Southern Peru Copper Corp., 343 F.3d 140 (2nd Cir. 2003) (Peruvian
plaintiffs brought personal injury claims under ATCA against American mining company,
alleging that pollution from mining company’s Peruvian operations had caused severe lung
disease); Abebe-Jira v. Negewo, 72 F.3d 844 (11th Cir.1996) (former prisoners in Ethiopia
filed lawsuit under ATCA against former Ethiopian official for torture); Kadic v. Karadzic,
70 F.3d 232 (2nd Cir.1995) (Bosnian plaintiffs brought suit against the self-proclaimed leader
of unrecognized Bosnian-Serbian entity under the ATCA for war crimes).
49 124 S.Ct. at 2739.

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international law. The case arose from the 1985 seizure of a Mexican national,
Humberto Alvarez-Machain, on suspicion of assisting in the torture of a Drug
Enforcement Agency (DEA) agent. When extradition attempts failed, the DEA
contracted with Mexican nationals, including Jose Francisco Sosa, to abduct
Alvarez-Machain from his home and bring him to the United States so he could be
arrested by federal officers.50 After a lengthy procedural challenge,51 Alvarez-Machain
was acquitted by the District Court. In 1993, he returned to Mexico and commenced
a civil suit against the United States and Sosa for his allegedly arbitrary arrest and
detention. The holding in Sosa clarifies when and whether the ATCA provides for a
cause of action on the basis of an alleged violation of customary international law.
The Supreme Court held that “some, but few” torts in violation of international
law are recognized under the ATCA.52 The Court stated that a legitimate ATCA claim
should “rest on a norm of international character accepted by the civilized world and
defined with a specificity comparable to the features of the 18th century paradigms we
have recognized [i.e., violations of safe conducts, infringement of the rights of
ambassadors, and piracy],” explaining that these norms are part of federal common
law.53 The Court declined to provide examples of other offenses that might provide
grounds for an ATCA, and counseled restraint in finding them,54 though the majority
opinion cites to Filartiga on a number of occasions, including citing in dicta to the
Filartiga Court’s finding that “for purposes of civil liability, the torturer has become
— like the pirate and slave trader before him — hostis humani generis, an enemy of
all mankind.”55 The Court did, however, conclude that two international agreements
that the United States is a party to that have been widely recognized as sources of
jurisprudence regarding customary international law — the Universal Declaration of
Human Rights and the International Convention on Civil and Political Rights — did
not in themselves constitute an international norm comparable to those fulfilling the
18th century-paradigm test.56 The application of customary international law in U.S.
courts, as least with respect to providing grounds for aliens to pursue civil claims under
the ATCA, appears quite limited in scope.57
50 Alvarez-Machain v. United States, 331 F.3d 604, 609 (9th Cir. 2003) (en banc).
51 See United States v. Alvarez-Machain, 504 U.S. 655 (1992).
52 Sosa, 124 S.Ct. at 2759.
53 Id. at 2761-62. See generally Beth Stephens, The Law of Our Land: Customary
International Law as Federal Law After Erie, 66 FORDHAM L. REV. 393, 402 (1997) (the
Framers were concerned with following international law to avoid creating causus belli for
a European power).
54 Sosa, 124 S.Ct. at 2761.
55 Id. at 2766.
56 Id. at 2767.
57 Id. The ATCA is a jurisdictional statute, providing federal courts with the authority to
entertain claims but not creating a statutory cause of action for aliens. Accordingly, whether
or not the ATCA provides federal jurisdiction over alien claims is dependant upon whether
the alleged offense of customary international law is recognized under federal common law.
See id. at 2758-65.

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Reference to Foreign Law by U.S. Courts
In recent years, foreign or international legal sources have increasingly been cited
by the Supreme Court when resolving domestic legal issues.58 While these sources
have been looked to for persuasive value, they have not been treated as binding
precedent upon U.S. courts. Reference to foreign law or jurisprudence is not a new
occurrence. For example, in 1815, the Supreme Court noted that “decisions of the
Courts of every country, so far as they are founded upon a law common to every
country, will be received, not as authority, but with respect.”59 With respect to
international law and treaty interpretation, at least, foreign practice and understanding
have always been considered to have persuasive value.60 However, domestic court
reference upon foreign law and practice has become increasingly controversial. There
is some dispute among scholars and policymakers over the extent to which American
courts can and should rely on foreign practices in making decisions interpreting U.S.
statutes and the Constitution, particularly following recent Supreme Court rulings that
referred to foreign jurisprudence.61
Possibly the most notable recent reference to foreign law by a U.S. court occurred
in the Supreme Court’s majority opinion in the 2003 case of Lawrence v. Texas, which
held that a Texas statute outlawing same-sex sodomy violated the Due Process Clause
of the 14th Amendment.62 In an earlier Court decision upholding anti-sodomy laws,
Bowers v. Hardwick, Chief Justice Burger had written that practices akin to those in
question in Lawrence had been prohibited throughout Western history.63 Writing for
the majority in Lawrence, Justice Kennedy responded to this claim by noting that
decisions by other nations and the European Court of Human Rights within the past
few decades conflicted with the reasoning and holding of Bowers. The Court’s opinion
58 See Vicki Jackson, Yes, Please, I’d Love to Talk With You, LEGAL AFFAIRS (Aug. 2004),
at 40 (“[o]f the current nine justices, at least six — Chief Justice Rehnquist, and Justices
John Paul Stevens, Antonin Scalia, Anthony Kennedy, Ruth Bader Ginsburg, and Stephen
Breyer — have...[cited to foreign law] since 1992")..
59 Thirty Hogsheads of Sugar v. Boyle, 13 U.S. (9 Cranch) 191 (1815).
60 See, e.g., Zicherman v. Korean Air Lines Co., Ltd., 516 U.S. 217 (1996) (Court
interpretation of international agreement aided by examining negotiating and drafting
history and the post-ratification understanding by contracting parties); I.N.S. v. Cardoza-
Fonseca, 480 U.S. 421, 439 n.22 (1987) (using U.N. interpretative materials to “provide
significant guidance in construing” the 1967 United Nations Protocol Relating to the Status
of Refugees); Air France v. Saks, 470 U.S. 392, 404 (1985) (finding that “the opinions of
our sister signatories to be entitled to considerable weight” when interpreting agreement
provisions); Sumitomo Shoji America, Inc. v. Avagliano, 457 U.S. 176, 184 n.10 (1981)
(position of Japanese government entitled to great weight when interpreting provisions of
U.S.-Japan treaty); Jordan v. Tashiro, 278 U.S. 123, 127 (1928) (finding that provisions of
treaties “should be liberally construed so as to effect the apparent intention of the parties to
secure equality and reciprocity between them”).
61 Compare Jackson, supra note 58, with Richard Posner, No Thanks, We Already Have Our
Own Laws, LEGAL AFFAIRS (Aug. 2004), at 43.
62 123 S.Ct. 2472 (2003).
63 478 U.S. 186, 192 (1986).

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went on to imply in dicta that trends in other countries’ understandings of “human
freedom” can inform our own, though the anti-sodomy statute was struck down on
separate grounds.64
It is not yet clear how persuasive foreign law is considered to be, or whether the
Court’s decision in Lawrence and other recent cases evidences a growing practice of
looking to foreign jurisprudence to inform domestic decisions.65 Thus far, it does not
appear that an American court has based its holding on a question of statutory or
Constitutional interpretation solely on foreign law. Although foreign law and practice
have historically had a role in American jurisprudence and courts will likely continue
to refer to it, where, when, and how significantly they will rely upon it is difficult to
predict.
64 Lawrence, 123 S.Ct. at 2483. In dissent, Justice Scalia referred to the majority’s
discussion of foreign law as “meaningless...[d]angerous dicta.” Id. at 2495 (Scalia, J.,
dissenting).
65 For a more detailed discussion on this subject, see Janet Koven Levit, Going Public with
Transnational Law: The 2002-2003 Supreme Court Term, 39 TULSA L. REV. 155 (2003).

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