This article aims to deepen our understanding of the dynamic interaction between language ideologies, education policies and teacher beliefs about monolingualism. This study takes place in Flanders (Belgium), a region which is characterized by educational policies based on a strong monolingual ideology. The research design combines document analysis, regarding recent language policies in Flemish education, and in-depth interviewing of teachers in secondary education. The main objective of this study is to examine how language policies in education are reflected in teacher beliefs in schools in secondary education. We will look at the interaction between the monolingual policies explicated by the Flemish policy makers and the beliefs of secondary education teachers on home language and language use. Finally, we want to gain more insight in the explanatory schemes teachers use to rationalize their monolingual beliefs. In conclusion implications for policy makers are discussed.