This book identifies over 5,500 HPSAs designated throughout the United States as of September 2005; multiple federal programs relied on these designations to allocate resources or provide benefits. We estimated that slightly more than half of the HPSAs were designated for geographic areas or population groups, and these geographic and population-group HPSAs were located in all 50 states and the District of Columbia. Facility HPSAs, which accounted for slightly less than half of the total number of HPSAs, were also located in every state and the District of Columbia. In fiscal year 2005, more than 30 federal programs-including programs administered by HRSA, CMS, and federal agencies outside of HHS-relied on HPSA designations and, in some cases, HPSA scores, to allocate resources or provide benefits. These included NHSC programs that award scholarships or educational loan repayment to students and health professionals in exchange for a commitment to practice in HPSAs for at least 2 years. Other programs relying on HPSA designations to allocate resources or provide benefits included programs that pay physicians bonus payments for services provided to Medicare beneficiaries in geographic HPSAs and programs that waive certain requirements for foreign physicians if they agree to practice in HPSAs or other underserved areas of the United States. The use of the HPSA designation by numerous federal programs to allocate resources or provide benefits is an incentive for obtaining and retaining a HPSA designation.