This article reports on an action research project in which the value of critical friendship for students doing research and writing their dissertations within an international master's course has been explored. This course is run jointly by Roehampton University (London, UK), Charles University (Prague, Czech Republic) together with Fontys OSO (Tilburg, the Netherlands). It describes the process and the results of working with the concept of critical friendship in this master's course since its start in 2005. Data were collected by means of various qualitative instruments and data sources: evaluation forms after tutorial sessions, reflective logs and focus interviews. The results show that the process of engaging with the research they did was enhanced and supported by the development of critical friendship groups. A number of recommendations have been formulated, such as the importance of discussing the concept of critical friend and its philosophy with the participants and of defining roles and tasks as clearly as possible. (Contains 1 note and 8 tables.)