This is a commentary paper in the volume on "Teachings situations as object of research: empirical studies within theoretical perspectives". An essential object of mathematics education research is the analysis of interactive teaching and learning processes in which mathematical knowledge is mediated and communicated. Such a research perspective on "processes of mathematical interaction" has to take care of the difficult relationship between mathematics education theory and everyday mathematics teaching practice. In this regard, the paper tries to relate the development in mathematics education research within the "theory of didactical situations" to developments in interaction theory and in the "epistemological analysis of mathematical communication".