The March-June 1999 NATO war over Kosovo raised questions about many issues affecting the future of NATO. Questions arising from the conflict about political objectives, strategy, command arrangements, NATO-Russian relations, allied capabilities, future enlargement, allied unity, non- Article V operations, and the response of potential adversaries remain under debate. This report provides brief "lessons learned" from Operation Allied Force . NATO had limited political objectives in the conflict, most of which were at least partially met. Key considerations, such as avoiding civilian casualties and losses to NATO forces, affected design of the military strategy supporting these objectives. NATO's restrained escalation of force, with no threat of ground attack and a gradual application of increased air power, violated conventional U.S. military doctrine to maximize shock. A desire to sustain allied unity largely caused this restraint, and ceded time and initiative to Milosevic. Subsequent proposals to streamline allied decision- making, including an "intervention committee," are discussed. Why Milosevic decided to accept NATO terms and withdraw his forces remains unclear. Damage caused by NATO bombing, sustained allied unity, possible allied planning for a ground war, a desire to preserve his forces, and desertion of Russia as a possible protector were likely principal reasons. NATO sought to maintain political engagement with Russia, which sharply opposed the air war. Russia sought to undermine NATO's objectives, but in the end acceded to allied desires to assist in achieving a diplomatic solution. The conflict revealed a significant gap in military capability between the United States and its allies, which were deficient in key areas such as lift, precision-guided munitions, and night combat. These shortfalls may have spurred European interest in developing greater capabilities, an interest not yet reflected in defense budgets. The three new allies gave political support to NATO goals, but did not send combat forces. Their restrained involvement raised issues for a possible next round of enlargement, such as candidate states' military preparedness and political will. NATO maintained unity, but a range of views was evident in allied governments. Leftist or center-left governments supported the conflict, Britain took a leading role, Italy bore a heavy burden, and the Greek government, despite vigorous popular opposition, maintained its political support for the war. The conflict broke new ground in that the allies went to war in part for humanitarian reasons. Potential adversaries learned that NATO may no longer regard claims of sovereignty as a shield against allied intervention in their affairs. They may also have learned useful lessons from Milosevic's tactics intended to divide the allies, and that NATO may be more likely to take decisive action to protect interests near Europe, than when interests at a greater distance are affected. This report, in the form of a memorandum, was originally prepared for Senator William Roth, and is being made available to Congress as a whole with his permission.