The study focuses on foreign language teachers’ immediate and broader environment and its influence on their professional development towards expertise from their own perspectives. The study was conducted within a research project dealing with the nature of expertise of foreign language teachers. Its last, third, phase, which we are to present in this study was diachronically oriented and aimed to explore the determinants of the development of foreign language teachers’ expertise. The data were collected in biographic interviews with 8 teachers at Czech lower secondary schools. Content analyses of verbal protocols based on theory-driven system of categories was used bringing some interesting results.