B ecause training and supervision, like psychotherapy itself, are inherently human and thus complex experiences, it is difficult to empirically investigate them and come to any definitive answers about their processes and associated outcomes. Nevertheless, the centrality of training and supervision to the delivery of psychotherapy makes reviewing the empirical findings an essential task in order to see what results may tell us about these vital endeavors.This chapter was inspired by our recent chapter (Knox & Hill, 2021). We added a few new studies, and rather than reviewing individual studies as we did in that chapter, we provide here summaries of findings. We explore the effectiveness of training and supervision with undergraduate and graduate student therapists-in-training and examine the factors contributing to the effectiveness of this training/supervision.When referring to training, we mean structured education for groups of trainees. In contrast, we define supervision as an individualized process of one supervisor working with one trainee (supervisee) regarding specific clients. We duly acknowledge that the distinction between training and supervision is sometimes unclear, in that training programs may include a supervision element and supervision may include structured teaching or group supervision formats.