Integrating science lessons with lessons in other content areas can be an efficient use of limited time, but not every activity can be integrated productively. Teachers must consider several factors when making decisions about which lessons to integrate: time available, specific curricular requirements in other content areas, and the interests of particular students to name a few. In this article, the authors discuss using the big ideas—concepts that can be applied to explain a variety of phenomena across contexts—to guide choices about integrating science across the content areas. This approach can help students develop lasting understanding about important scientific ideas.