Evaluation is often described as an essential tool for achieving socioeconomic development, good governance, sustainability and equity. The value of evaluation itself is taken for granted. This introductory chapter emphasizes the need for a critical discussion – also about evaluation itself. Evaluation is a specific social practice which was constructed at a certain time and in a specific environment. The diffusion of evaluation has therefore also meant a diffusion of specific notions about politics, implementation, societal development, policy development, public administration and so on. The chapter examines these notions and raises questions about their future relevance. The chapter argues that the expansion of evaluation impacts what we see as valid arguments in discussing policy options, how decisions should be made, what we regard as evidence, how we define success and failures and a lot more. The practice of evaluation is therefore not only based on certain notions; it also has interactive societal effects and impacts how we conceive concepts and categories which form our understanding of society. The chapter further highlights the importance of the interplay between different stakeholders and interests involved in the evaluation enterprise – the power aspect of the evaluation enterprise and the role of the evaluation societies.