Our study responds to calls for theory-driven approaches to studying innovation diffusion processes in health care. While most research on diffusion in health care is situated at the service delivery level, we study innovations and associated processes that have diffused to the system level, and refer to work on complex adaptive systems and whole systems change to guide our work. System-level diffusion not only involves the spread of innovations across sector boundaries in a system, it may alter interactions and care delivery within multiple system components, change the nature of the interdependencies between components, and ultimately lead to whole systems change.