The past two decades research on teachers' professional development focusses increasingly on professional learning communities (PLCs). Based on a literature search a conceptual framework was developed including a comprehensive PLC-concept. Comprehensive because it takes into account the complexity of the educational context. The PLC-concept outlining 11 characteristics, is embedded in a framework, containing five external factors that influence. The framework was evaluated by interviewing educational experts. The literature search and the interviews showed a great diversity of distinct PLC characteristics and a wide range of external influencing factors. Based on expert interviews, no essential elements appeared to be lacking in the framework, moreover no other perspectives on the framework were mentioned. An additional search on recent literature confirmed the constructed framework. As yet we concluded that the developed concept is sufficiently comprehensive and feasible for conducting research on PLCs.