For a long time I've been using the phrase 'theory of change' to express the idea that a project is essentially a social experiment, and that M&E is about testing the hypotheses implicit in the social experiment.  Recently I was challenged to succinctly ellaborate what I thought embodied the 'theory of change' approach.  The following points provide an overivew of the concept, and the practical and philosophical elements, as I see them: THEORY OF CHANGE Broad Concept International aid projects exist to create social change.  Any project implicitly aligns with a ‘theory’ about how desirable social change might be achieved—a ‘theory of change’.  To bring about social change, human actors interact within a social system through time. A role of project design is to articulate the ‘theory’—the temporal sequence of relationships, and how these are expected to influence desirable change. A role of M&E is to test ...