This report summarizes the findings of a study performed by the Institute for Defense Analyses to advise the Deputy Secretary of Defense regarding Defense Agency management issues that warrant the attention of DoD's senior leadership in preparation for the FY 2001 Quadrennial Defense Review. The study covered fourteen of the Agencies, which in total account for 20 percent of DoD's budget. IDA assessment teams met with Agency officials, review Agency plans and programs, interviewed Agency customers, and examined available information on Agency performance. The report provides a comprehensive review of each Agency's mission, history, management initiatives, and performance. We find that the current assignment of functions to the Defense Agencies is consistent with DoD's missions and policies. At the same time, fixing five DoD-wide management problems would improve the performance of DoD support functions, strengthen working relationships between the Agencies and their customers, and yield significant savings. Needed initiatives for making these changes are described.