Context: The evaluation of training is problematic and the evidence base inconclusive. This situation may arise for 2 main reasons: training is not understood as a complex intervention and, related to this, the evaluation methods applied are often overly simplistic.
Method: This paper makes the case for construing training, especially in the field of specialist medical education, as a complex intervention. It also selectively reviews the available literature in order to match evaluative techniques with the demonstrated complexity.
Conclusions: Construing training as a complex intervention can provide a framework for selecting the most appropriate methodology to evaluate a given training intervention and to appraise the evidence base for training fairly, choosing from among both quantitative and qualitative approaches and applying measurement at multiple levels of training impact.