As an increasing number of multilingual children are enrolled in European schools, it is important to gain more insight into teachers' attitudes towards multilingual approaches in education. The goal of this study is to investigate the attitudes of primary school teachers in Greece, Italy and the Netherlands, three countries that have a highly multilingual student population but differ with respect to the migration context and language policies. Using an online questionnaire, we assessed teachers' attitudes towards multilingualism in the school environment and their adherence to monolingual ideals. We aimed to compare the three countries and investigate which factors related to the teachers' background and school characteristics predict teachers' beliefs. The results suggest that teachers in Greece are significantly more positive towards multilingualism than teachers in Italy and the Netherlands, despite great individual variation. Moreover, for all three countries, we found that having received training on multilingualism had a positive effect on teachers' attitudes. In the Netherlands, we found that teachers who taught a greater proportion of multilingual students on average showed more positive attitudes towards multilingualism. We discuss the implications of these findings for educational language policy, highlighting the importance of evidence-based training on multilingualism for all teachers.