Over the last three decades, the concept of teacher collaboration has been embraced as a promising concept in the sphere of educational policy and educational research. Teacher collaboration is now considered crucial to strengthening the position of teachers, shaping their professional space and improving their professionalism. However, the concept of teacher collaboration lacks consensus: both its definitions and its purpose are the subject of discussion and criticism. Against this background, we present a theoretical and empirical analysis of teacher collaboration. We carried out secondary analyses on existing data from a large quantitative study conducted in primary schools ("n" = 271) and secondary schools ("n" = 343) to examine the extent to which teachers collaborate and to identify organizational characteristics and teachers' personal characteristics that affect teacher collaboration. The models we developed using structural equation modelling reveal that teacher collaboration in primary schools is influenced by the extent to which teachers perceive school-leader support, teachers' satisfaction concerning their participation in decision making and teachers' orientation towards student performance. The model for secondary schools is more straightforward: only perceived school-leader support directly influences teacher collaboration.