Biomedical research in the United States has contributed enormous- ly to science and human health and is conducted in several thousand institutions that vary widely in their histories, missions, operations, size, and cultures. Though these institutional differences have important consequences for the research they conduct, the organizational taxonomy of US biomedical research has received scant systematic attention. Consequently, many observers and even participants are surprisingly un- aware of important distinguishing attributes of these diverse institutions. This essay provides a high-level taxonomy of the institutional ecosystem of US biomedical re- search; illustrates key features of the ecosystem through portraits of eight institutions of varying age, size, culture, and missions, each representing a much larger class exhibiting additional diversity; and suggests topics for future research into the research output of institutional types that will be required to develop novel approaches to improving the function of the ecosystem.