While in recent years substantial efforts have been made to promote and disseminate (quantitative) counter-factual impact evaluation practice there is much less sharing of good practice concerning so-called theory-based impact evaluation. However, while counter-factual impact evaluation can tell us how much impact an intervention makes, theory-based impact evaluation is crucial to increasing our understanding of why certain interventions work or do not work. Without this understanding, it is impossible to improve interventions. In addition, in many cases counter-factual impact evaluation is not actually a viable method, and then theory-based evaluation can still inform how the intervention is contributing to change.  This seminar will therefore focus on this theory-based impact evaluation, drawing on the latest advances made in terms of methodology. The most cited methods – Process Tracing, Congruence Analysis, Qualitative Comparative Analysis, Pawson and Tilley’s Realist Evaluation, Mayne’s Contribution Analysis – will all be covered and put into perspective. Several cases will be used to exemplify these methods. The seminar participants will also undertake a number of exercises to better understand the methods. An important focus of the course will be to show how theory-based impact evaluation can match the rigour associated with counter-factual impact evaluation.  The seminar is aimed at those experienced in impact evaluation who wish to further advance their capability in this field.