Legitimate knowledge claims about causation have been a central concern among evaluators and applied researchers for several decades and often have been the subject of heated debates. In recent years these debates have resurfaced with a renewed intensity, due in part to the priority currently being given to randomized experiments by many funders of evaluation studies, such as the Institute for Educational Sciences. In this dialogue, which took place at Western Michigan University in October 2008, two of the field's leading theorists and methodologists, Thomas D. Cook and Michael Scriven, described their current thinking and views about causation and causal inference in evaluation. They also discussed recent methodological developments for cause-probing investigations that sometimes produce results comparable to those produced by randomized experiments. Both Cook and Scriven prepared clarifying postscripts after reading the edited transcript.