This paper provides an overview of the current manpower structure in the United States and NATO Europe. The authors compare the levels and composition of active and reserve forces, and discuss current demographic trends and potential problems for recruiting and retaining qualified personnel. They also present a paradigm for evaluating available options for supplying military personnel, and evaluate research on the comparative cost-effectiveness of these alternatives. A combination of factors has increased the pressure on manpower planners. Evolving military technologies have increased the demand for the most highly qualified segments of the youth population. Policymakers are faced with a declining youth cohort and increases in the civilian opportunities available to potential enlistees. These trends may require changes in manpower policies. Whether unfavorable demographic trends will make it difficult to meet future requirements or dramatic changes in the political environment reduce manpower needs, policymakers in the United States and NATO Europe will have to evaluate alternative enlistment programs.