Realist evaluation has gained prominence in the field of evaluation in recent years. Its theory-driven approach to explaining how and why programmes work or not makes it attractive to many novices, early career researchers, and organizations implementing various programmes globally and relevant to policymakers and programme implementers. While realist evaluation seeks to be pragmatic, adopting principles and methods that can be used to help focus an evaluation, its deep ontological and epistemological foundations make its application in real-life situations challenging. In (...) this paper, we seek to unpack the key tenets scaffolding the practical application of realist evaluation. Although Pawson and Tilley foreground realist evaluation in applied scientific realism, we argue that an amalgam of scientific and critical realist principles underpins realist evaluation. We unpack these principles and illustrate how they fit into each other to provide a cogent theoretical foundation for realist evaluation. (shrink)