The size of the private rented housing sector (PRS) varies markedly between coun-tries. The paper explores the role of policy in supporting the PRS with emphasis on the evidence from France, Germany, the UK and the USA. The definition and meas-urement of the size of the sector in each country is considered. A key issue that is explored is the effect of policies on the demand for private renting and investment in the sector. The roles of subsidies, taxation and regulation are considered in the con-text of the housing systems of particular countries. The analysis is important in un-derstanding current tenure distribution and is relevant to evaluating policies that seek to increase the size of the sector. The paper draws on some of the evidence in the authors’ research report for the English Department of Communities and Local Government: Promoting Investment in Private Rented Housing Supply: International Policy Comparisons (November 2010). See: http://www.communities.gov.uk/publications/housing/investprivaterentedhousing