AbstractThe literature on patient public involvement and engagement (PPIE) in health research has grown significantly in the last decade, with a diverse range of definitions and topologies promulgated. This has led to disputes over what the central functions and purpose of PPIE in health research is, and this in turn makes it difficult to assess and evaluate PPIE in practice. This paper argues that the most important function of PPIE is the attempt to make health research more democratic. Bringing this function to the fore and locating PPIE in the wider context of changes in contemporary forms of democratic engagement provides greater conceptual clarity over what PPIE in research should be trying to achieve. Conceptualizing PPIE as a form of democratization has a number of benefits. First, theories of what are appropriate, normatively justifiable and workable criteria for PPIE practices can be developed, and this can provide tools to address the legitimacy and accountability questions that have troubled the PPIE community. Second, this work can be used to form the basis of a research agenda to investigate how PPIE in health research operates, and how it can facilitate and/or improve democratic processes in health research.