The internship is a crucial component of principal preparation. This systematic research review aims to build on two prior syntheses of existing research on principal internships. We employed an exhaustive review of five search engines for empirical studies on principal internships in the United States between 2010 and 2023. Our search yielded 92 studies. We extracted key characteristics from each study as well as the main findings. We distributed the findings across the following themes: policy, program redesign, program value, diverse perspectives, coaching and mentoring, internship activities, and internship effects. The literature on internship policy, diverse perspectives, and internship activities is relatively limited. In contrast, there was much more research on program redesign and value, coaching and mentoring, and internship effects. We conclude the review by comparing our findings to two prior research reviews and offering recommendations for future research and practice.