Using interpersonal skills is an important part of humane and effective investigative interviewing for police. Training police in these skills varies in its contents and amount between countries and police forces. This review explores how interpersonal skills are defined and assessed in the context of interview training for police. A systematic evaluation resulted in 26 studies meeting the inclusion criteria. The most trained interpersonal skills were rapport (n = 18 studies), and active listening (n = 2 studies). Studies also evaluated training environments (n = 3 studies), and adherence to or knowledge of specific interviewing protocols (e.g. PEACE, n = 1; Whole Story framework, n = 1, procedural justice, n = 1). The reported effects of training vary with half of the included studies (n = 13) reporting positive effects while the other half (n = 13) reported limited or no effects. We discuss how conceptual definitions and study designs affect assessment of training outcomes. Aspects of training assessments (e.g. use of mock-interviews, self-reports, and lack of long-term follow-ups in the field) are discussed. We also discuss the need for more systematic research on training interpersonal skills for interviewing. Our findings should guide and inform further research on the topic.