The tutor role in problem-based learning (PBL) has attracted the interest of many researchers and has led to an abundance of studies. This article reports on major trends in studies investigating the tutor during the past 10 years. Three major trends were observed by the authors while analysing the studies conducted: studies on the differential influence of content expert and non-content expert tutors on student achievement, studies on process variables, and studies on the relationship between tutor characteristics and differential contextual circumstances. The aim of this article is to summarize the main findings of the studies conducted so far within the three trends observed, to provide directions for educational practitioners and policy makers, and to suggest directions for future research questions. The studies included were selected by conducting a literature search in medical journals, which was complemented with the personal archives of the authors. The results of the studies conducted within the three trends of research have led to advanced insights in tutoring. The outcomes revealed that content expert tutors tend to use their subject-matter expertise more to direct the discussion in the tutorial group, whereas non-content expert tutors tend to use their process-facilitation expertise more to direct the tutorial group. Furthermore, a tutor's performance is not a stable characteristic but is partly situation specific. It is concluded that a tutor should both know how to deal with the subject matter expertise and should know how to facilitate the learning process. Faculty and policy makers should put substantial efforts into designing curricula and cases and developing tutors' skills by faculty development strategies that stimulate reflection. The research agenda should be driven more by modern educational theories of learning in which tutoring is a process aimed at stimulating constructive, self-directed, situated and collaborative learning by students. Furthermore, more qualitative studies should be conducted to gain better insights in teachers' conceptions about the tutor role and student learning to better understand their behaviours.