Both speakers at the Eleanor Chelimsky Forum on Theory and Practice in Evaluation pointed out the complexity and messiness of evaluation practice, and thus potential limits on theory and generalizable knowledge. The concept of reflective practice offers one way forward to build evaluation theory. Building generalizable knowledge about practice depends on the ability of expert practitioners to dialogue at greater length about the issues they encounter. On that basis they can better develop the implications of their practice experiences for evaluation theory. By renewing attention to what program managers and service practitioners know, we can also build evaluation theory, because their reflective practice can inform both the program and knowledge (external validity) dimensions of theory.