BACKGROUND: There is no commonly accepted comprehensive framework for describing the practical specifics of external support for practice change. Our goal was to develop such a taxonomy that could be used by both external groups or researchers and health care leaders. METHODS: The leaders of 8 grants from Agency for Research and Quality for the EvidenceNOW study of improving cardiovascular preventive services in over 1500 primary care practices nationwide worked collaboratively over 18 months to develop descriptions of key domains that might comprehensively characterize any external support intervention. Combining literature reviews with our practical experiences in this initiative and past work, we aimed to define these domains and recommend measures for them. RESULTS: The taxonomy includes 1 domain to specify the conceptual model(s) on which an intervention is built and another to specify the types of support strategies used. Another 5 domains provide specifics about the dose/mode of that support, the types of change process and care process changes that are encouraged, and the degree to which the strategies are prescriptive and standardized. A model was created to illustrate how the domains fit together and how they would respond to practice needs and reactions. CONCLUSIONS: This taxonomy and its use in more consistently documenting and characterizing external support interventions should facilitate communication and synergies between 3 areas (quality improvement, practice change research, and implementation science) that have historically tended to work independently. The taxonomy was designed to be as useful for practices or health systems managing change as it is for research.