The U.S. Army has moved along the path of preparing for the 21st century. This process began with the conceptual examinations and assessments carried out under the "Louisiana Maneuvers" and the Army's Battle Labs, and matured through the Force XXI process. The Army recently completed its first series of Advanced Warfighting Experiments that will shape the redesign and restructure of the future force, Army XXI, for the early years of the new millennium. While the broad outlines of Army XXI have been sketched out, many of the details remain to be filled in. Undoubtedly, these efforts will be influenced by the recent reports of the Quadrennial Defense Review (May 1997) and the National Defense Panel (December 1997). Indeed, debates over details of the force structure and the ultimate size of the Army are not likely to abate any time soon. To assist in the further conceptual development, Dr. William T. Johnsen places Army XXI in a broad strategic context. He briefly examines the anticipated international security environment and the roles that the U.S. Armed Forces and the Army can be expected to perform. He then assesses a wide range of general factors that will influence the capabilities needed to carry out the anticipated roles. Finally, he examines general and specific criteria that can be used to determine the appropriate size of Army XXI. Dr. Johnsen's conclusions are likely to spur further debate on the force structures of Army XXI. These debates are essential if the U.S. Army is to be prepared to carry out its future roles. It is in this context that the Strategic Studies Institute offers this contribution to the dialogue.