DLESE is the Digital Library for Earth System Education, a geoscience community resource that supports teaching and learning about the Earth system. It is funded by the National Science Foundation and is being built by a community of educators, students, and scientists to support Earth system education at all levels and in both formal and informal settings. Resources in DLESE include lesson plans, scientific data, visualizations, interactive computer models, and virtual field trips - in short, any web-accessible teaching or learning material. Many of these resources are organized in collections, or groups of related resources that reflect a coherent, focused theme. In many ways, digital collections are analogous to collections in traditional bricks-and-mortar libraries.