Debate over reforming the nation's healthcare system has stimulated a need for health services research (HSR) models that are nationally applicable. Toward this end, the authors identify the Military Health System (MHS) as America's "undiscovered" laboratory for HSR. Although many may confuse the MHS with the Department of Veterans Affairs (VA), the 2 systems vary dramatically with respect to their beneficiary populations, access to care, and other important attributes. In this article, the authors describe key characteristics of the MHS including its large beneficiary base, its direct care operating environment, its dedicated medical school and graduate education programs, and its fully operational integrated health information system. Although a few health systems (eg, Kaiser Permanente, Partners Healthcare, and Department of Veterans Affairs) possess some characteristics, no other has all of these components in place. This article sets the stage for contemporary HSR studies with broad applicability to current issues in American healthcare that could be performed within the MHS. Inclusion of the MHS environment in HSR studies of health services delivery modalities, adoption of health information technology, access to care, relationship of medical education to effective safe care delivery, health disparities, child health, and behavioral health would provide strong underpinnings for proposed changes in American healthcare delivery. Finally, the article highlights current regulatory barriers to research within the MHS whereas suggesting steps to minimize their impact in conducting HSR.