An increasingly globalised world has led to great language diversity in institutional settings. Sweden is no exception; 3 of 10 students in compulsory school have a migrant background. Increased diversity may result in challenges, e.g. knowing how to balance the use of the target language with other languages represented among the students to facilitate learning and interaction. As educational policy documents for Swedish schools offer little guidance, teachers of English as a foreign/second language (L2) are left to their own devices regarding what language(s) to draw on in instruction. With the aim of developing an empirical knowledge base about teacher beliefs and practices in multilingual L2 English classrooms in Sweden, a web-based questionnaire was distributed to a stratified random sample representative of secondary-school teachers (N = 139). The questionnaire was designed to target six salient constructs related to multilingual teaching/learning conditions. Quantitative data analyses revealed that although multilingualism is perceived as a resource, there was greater variation in teachers’ perceptions of the role of students’ L1s in learning and teaching, and whether to exclusively use English when teaching. Furthermore, the participants strongly support the Swedish policy of offering mother-tongue instruction at school, which has been in place over the past five decades.