This paper describes an analysis of facilitation of a student-centered problem-based learning group. The focus of this analysis was to understand the goals and strategies of an expert facilitator in support of collaborative learning. This was accomplished through interaction analysis using video data and stimulated recall to examine two PBL group meetings. In this paper, we examine how specific strategies were used to support the PBL goals of helping students construct causal explanations, reason effectively, and become self-directed learners while maintaining a student-centered learning process. Being able to articulate these strategies is an important step in helping others learn the art of PBL facilitation.