Although the U. S. Air Force emerged as a separate military arm of the government only a quarter of a century ago, its history goes back to the Civil War when the Union Army sent men aloft in balloons to observe the movements of the Confederate Army. Documents dealing with these early "air operations in the department of aeronautics"-as well as the subsequent activities of successor aeronautical agencies including the Air Force-are preserved in several dozen public and private repositories -throughout the nation. They include not only the official government documents on the Air Force but also the personal papers of individuals who helped develop the service and those of military commanders and pilots who flew into combat in two World Wars, Korea, and Vietnam. This guide seeks to aid scholars and researchers to locate collections of primary and secondary documents on the Air Force. The first part deals with official Air Force depositories, which are essential to the historian writing about its operations worldwide. The second part describes the equally important collections of the National Archives and its depositories, including the pertinent papers in the Presidential Libraries. The third part covers university and college collections of personal papers of various military and civilian leaders, as well as other documents, which deal with the Air Force. Other governmental depositories-federal, state, and local-plus a number of private collections where Air Force material may be found are listed in part four. Finally, the last section describes a variety of other collections where primary and secondary materials on military, naval, and civil aviation-which directly or indirectly have impinged on the development of the Air Force-may be found. This guide was compiled by Mr. Lawrence J. Paszek of the Office of Air Force History. Information for it was solicited from archivists, museum curators, and librarians in the Air Force and other government agencies, in universities, historical societies, and public libraries. Some depositories may have been unknowingly omitted, while information on holdings of others is not as complete as a researcher may desire. All assistance provided has been greatly appreciated, since preparation of this guide would have been impossible without the excellent cooperation of the officials and staffs of depositories. Air Force field historians and the cadets of the Air Force Reserve Officers Training Corps (AFROTC) detachments throughout the United States also responded generously to appeals to search and describe manuscript collections in their universities or areas. Personnel of several depositories reviewed pertinent portions of the manuscript and offered valuable suggestions regarding their collections. Dr. Maurer Maurer, Chief, the Albert F. Simpson Historical Research Center, Maxwell AFB, Ala., and Dr. E. G. Campbell of the National Archives, Washington, D. C., commented on major sections of the manuscript. Within the Office of Air Force History, almost all staff members assisted with comments and suggestions, but especially significant contributions were made by Dr. Thomas G. Belden, Mr. Carl Berger, and Mrs. Mary Ann Cresswell.