The last 20 years have seen significant international shifts towards greater patient and public involvement (PPI) in health research and development (R and D). In England, then first health R and D strategy in 1991 did not mention PPI. Twenty years later, PPI is deeply embedded within the National Institute for Health Research. This article examines the evolving relationship between evidence and policy on PPI in research through a documentary analysis of English health R and D policy documents published between 1991 and 2010. It then considers what model of the research-policy interface best explains the expansion of PPI in research and why this is important.