The 1999 military operation against the Yugoslav Army in Kosovo suggests several areas in which Joint military operations were deficient. This study examined all aspects of the Kosovo conflict, including its political and historical underpinnings, in an attempt to understand these deficiencies and to recommend improvements. This document--provided in both a classified and unclassified version--is based on extensive original source documents and interviews with most of the principal participants, and serves as the definitive Army record on Kosovo. While the primary focus of the research was on U.S. Army involvement, it covered many other aspects of Operation Allied Force. Topics included NATO objectives in Operation Allied Force, air and ground planning, evolution of the air operation and its effects on fielded Yugoslav forces, Task Force Hawk, and peace operations.