Completion of a master's degree has changed significantly from being the specific responsibility of the candidate and his/her supervisor to being the responsibility of the whole educational institution. As a consequence, we have initiated an internal training course for professional development related to the supervision of master's theses. In this article, we outline the course and the participants' experiences and reflections. Further, the results are analyzed and discussed. We use the analytical framework of the concept of "professional learning communities" (Stoll et al., 2006), and action learning as a tool to implement ideas on professional learning. The course itself was divided into two separate phases: one combined (shared) training phase and one phase where supervisors were divided into forums to discuss authentic situations arising from forum members' supervision. The results indicate that the course as a whole was successful in promoting the professional development and collective learning of the academic staff.