The Department of Defense (DOD), which includes the military services, selects mid- to upper-career-level military officers to participate in fellowship and training-with-industry programs conducted at non-DOD organizations such as universities, think tanks, private corporations, federal agencies, and Congress. For some fellowships, the military departments pay a fee or tuition to the host organization. GAO was directed to review DOD's use of these programs. GAO's objectives were to determine: (1) the statutory provisions that authorize DOD's fellowship and training-with-industry programs for military officers, (2) the extent of the Office of the Secretary of Defense's (OSD) visibility over these programs, and (3) the extent to which the services are able to determine that they derive benefits from these programs. GAO analyzed relevant laws and DOD policies, collected data, and interviewed OSD and military service officials on their oversight and management roles and responsibilities for these programs. GAO is making 11 recommendations to DOD for improving oversight and management of DOD's fellowship and training-with-industry programs--for example, submitting DOD-required annual reports and performing service-required program reviews--that would enhance OSD's visibility over the programs and better position DOD to determine the extent to which it derives benefits from them. In response to a draft of this report, DOD concurred with the 11 recommendations and stated its action plan to implement the recommendations. Appended are: (1) Scope and Methodology; (2) Life-cycle Phases of a Fellowship Program; (3) Military Service Guidance on Fellowship and Training-with-Industry Programs; (4) Ethics Guidance Provided to Fellows; (5) Comments from the Department of Defense; and (6) GAO Contact and Staff Acknowledgments. (Contains 5 tables, 2 figures and 69 footnotes.)