Inquiries into the state of mathematics and science education in Australia express the need to make curriculum and teaching practices more relevant and meaningful to students' lives. This vision requires that teachers understand how relevance can enter the classroom in meaningful, appropriate, and subject-specific ways. In this paper I use interview data and classroom excerpts to explore junior secondary teachers' responses to what I call a "relevance imperative". The data shows that relevance is a multi-faceted construct that is constructed differently by teachers depending on their socio-historical experience with the subject culture. Implications for teachers teaching out-of-field and how we conceive of teachers as subject specialists are discussed, and suggestions for future research are given. (Contains 2 tables and 1 figure.)