This document is a thematic report that provides an overview of public participation in health research. The report is part of a series available from RAND Europe's Observatory on Health Research Systems. The purpose of the document is to provide non-specialists with an overview of the evolution and development of participatory health research across a range of economically developed countries. The report is divided broadly into two parts. The first part addresses the rationale for involving lay participants in health research in the first place, and explores some of the drivers underpinning recent moves to bolster participatory research methods. It also highlights some of the advantages and disadvantages of participatory approaches. The second part includes a series of country case studies, covering current patient and service-user involvement practices in Australia, Canada, the Netherlands, the United Kingdom, and the United States. The report concludes with a review of some options available to policymakers looking to boost or improve current practices, and an outline of further research needs. The report will be of interest to government officials dealing with health research policy, medical research councils, health research charities, institutions hosting health research projects, researchers, and patients and service users themselves.