In this introductory article, a brief history and introduction to contribution analysis is provided to lay the stage for the articles that follow. At the heart of contribution analysis is the aim to be able to make credible causal claims about the contribution an intervention is making to observed results. The key role that theories of change play is noted, and what a useful theory of change ought to contain is discussed. The article then makes a link between the philosophical discussions on causality and contribution analysis through a discussion of contributory causes. It is argued that such causes, which on their own are neither necessary nor sufficient, represent the kind of contribution role that many interventions play: where there are a number of other influencing events and conditions at work in addition to the intervention of interest. Contribution analysis is an approach to confirming that an intervention is a contributory cause.