This policy paper provides an overview of OECD work on measuring the extent and impact of public support for R&D through tax incentives. It discusses the policy rationale for tax incentives in the broader context of public support for business R&D, describing the main features of different modes of expenditure-based tax relief for R&D. It presents evidence on how much financial support is provided through tax incentives, how this has evolved in recent years and the variation in implied R&D tax subsidy rates across OECD countries and partner economies. The document also reviews empirical evidence on the impact of tax incentives, covering in detail different categories of impacts including potentially unintended effects. It further includes evidence on the use and impacts of income-based R&D tax incentives. The paper concludes with a synthesis of the main policy recommendations contained in key OECD policy documents and highlights future measurement and analytical work planned in this area.