This article reports on a two-year study of a self-study research group facilitation. The research group was designed as a professional development project in which six experienced teacher educators investigated their practices using a self-study approach. The pedagogical rationale of the facilitation was based on four broadly shared theoretical principles on how teacher educators can effectively work on their professional development. These theoretical principles were translated in a series of propositions ("if … then …") making clear the implications these principles held for the interventions of facilitators of teacher educator professional development. Qualitative content analysis of the audiotapes of the research group meetings, the facilitators' logbooks and all the written materials produced during the project serves as an empirical validation and refinement of these principles. The findings are presented as amendments to the original propositions. By interpretatively discussing why these propositions functioned as they did in practice, we contribute to the development of a pedagogy of teacher educator professional development.