Prepared as background for the OHE Commission on Competition, this paper provides an overview of the published literature detailing the links between quality and competition in health care systems.  It finds that most empirical research to date has focused on aspects of competition and quality in the hospital sector, rather than GP/outpatient care. The paper concludes that, overall, evidence about the effects of competition on quality provides no clear answers. Moreover, since the bulk of the research that is available has been done in the US, results are not necessarily applicable in the NHS setting.