In this third installment of our review on the science of training, we examine empirical articles associated with two pan-training areas, supervision and competency, before considering the capstone predoctoral training experience of internship. Critical issues considered include supervision effectiveness, differences and diversity in supervision, competency assessment, competency problems, internship match, and internship training. We offer conclusions and discuss intersecting implications across these areas (e.g., changes to the internship application to reflect norm-referenced assessments of competency by supervisors). We reiterate our call for a decrease in tribalistic rhetoric and a sharpened focus on curating an evidence-based approach to training. To that end, we advocate for greater stewardship concerning the science of training. We encourage directors of health services psychology training programs to disseminate program evaluation efforts into the peer-reviewed literature. We also encourage accrediting bodies to more clearly ground regulations in an empirically derived evidence-base. We conclude by proposing a recurrent conference designed to provide (a) pragmatic assistance to directors in transforming program evaluations into submission ready articles for dissemination into the peer-reviewed literature, (b) a venue for establishing collaborative research that builds on data accumulated across programs, and (c) opportunities for learning necessary methodological or analytic skills.