Co-teaching has become a well-known way of working among Finnish teachers in recent years. Teachers' collaboration is becoming increasingly important in light of the rising number of diverse students in regular classes. In an ideal co-teaching context, teachers collaborate as equals, recognise and respect each other's skills and competencies, and strengthen and support each other. In this study, we examine teachers' views on co-teaching and investigate which background factors explain teachers' views concerning the benefits and the challenges of co-teaching. The data obtained from Finnish basic education teachers' (N = 694) responses to an online questionnaire are analysed quantitatively. The results show some differences among the teachers' views. Subject teachers perceive more challenges in co-teaching than class and special education teachers. Class teachers perceive the fewest challenges. Although teachers are generally interested in co-teaching and some of them co-teach regularly, they also report several barriers to its application. The explanatory factors concerning the differences in teachers' views are gender, teachers' co-teaching experiences, the amount of co-teaching per week and working as a class teacher.