This is a copy of a book chapter for an unidentified book. Realist evaluation is a species of theory-driven evaluation. Programmes are shaped by a vision of change and they succeed or fail according to the veracity of that vision. Evaluation, by these lights, has the task of testing out the underlying programme theories. When one evaluates realistically one always returns to the core theories about how a programme is supposed to work and then interrogates it - is that basic plan sound, plausible, durable, practical and, above all, valid? Realist evaluations asks not, ‘What works?’ or, ‘Does this program work?’ but asks instead, ‘What works for whom in what circumstances and in what respects, and how?’
