Innovation is central to improvements in living standards and can affect individuals, institutions, entire economic sectors, and countries in multiple ways. Sound measurement of innovation and the use of innovation data in research can help policy makers better understand economic and social changes, assess the contribution of innovation to social and economic goals, and monitor and evaluate the effectiveness and efficiency of their policies. Since 1992, the Oslo Manual has been the international standard of reference for conceptualising and measuring innovation. It has since been revised on three occasions to account for growing levels of adoption and address evolving user needs. The manual provides the basis for a common language to discuss innovation, the factors supporting innovation, and innovation outcomes. This chapter sets out the rationale for measuring innovation and summarises the objectives pursued by this edition of the manual. The chapter outlines the contents of the manual and highlights the main definitions and other major novelties introduced in this edition. The chapter concludes with an overview of the main implementation challenges amidst a context of digital transformation of our economies and societies.