Peer-to-peer transactions have long played a role in commerce, but today's online platforms enable them on a much greater scale. Early examples include platforms for the sale of goods (e.g. online auction sites). Newer models include the rental of short-term accommodation and transport or mobility services. Sometimes described as the "sharing" economy or "collaborative consumption," this report refers to these innovative businesses as "peer platform markets." In addition to bringing benefits, peer platform markets raise new policy challenges, including consumer protection issues. As a general principle, consumer laws should be considered to apply to the basic offer of services to peers by peer platforms. It can be difficult, however, to apply existing laws to business models that blur the boundaries between consumers and businesses. What is the best approach to provide effective consumer protection while encouraging innovation? This report provides context for considering this and related questions.