In this chapter, the authors discuss teachers' perspectives on science and literacy integration in secondary classrooms. Beginning with teacher belief, the authors posit that teachers must first believe in the value of science and literacy integration to themselves, their students, or to district, curriculum, or assessment goals in order to implement integration. After belief in the value of integration is established, teachers vary in their approaches to implementation. Analysis of focus group data from middle and high school English language arts (ELA) and science teachers reveals patterns in frequency, strategies, and barriers to integration by subject area. In conclusion, the authors offer a framework for integration that explains teachers' approaches to integration at the classroom and team levels and suggests methods for advancing science and literacy integration.