In the Nordic countries, teacher education programmes are shifting towards a research-based design, thus placing new expectations and requirements on teacher educators. In this study, we aim to explore teacher educators' understanding of professional knowledge in research-based teacher education. We interviewed 16 Norwegian and six Finnish teacher educators. The teacher educators' views of professional knowledge could be divided into two main categories -- academic characteristics and personal characteristics -- and three dichotomies were discussed: educational sciences versus subject sciences, research versus teaching and collaboration versus autonomy. Teacher educators come from various backgrounds and bring different experiences into teacher education. Thus, their understanding of professional knowledge in research-based teacher education seems to be dichotomous and multifaceted. The dichotomies that were uncovered and the tensions between them provide the foundation for further development of teacher education in Norway and Finland.