Although frequently discussed in the evaluation literature and general agreement on what a theory of change is conceptually, there is actually little agreement beyond the big picture of just what a theory of change comprises, what does it show, how it can be represented and how it can be used.

This article outlines models for theories of change and their development that have proven quite useful for both straightforward and more complex interventions. The models are intuitive, flexible, well-defined in terms of their components and link directly to rigorous models of causality. The models provide a structured framework for developing a theory of change and analysing the intervention it represents.

This article presents and describes a robust and useful model for theories of change for simple and more complex interventions. It first outlines a basic generic theory of change, followed by a discussion of causation in relation to theories of change. Models for more complex multifaceted interventions are then presented, along with a discussion of nested theories of change.