The representation of collections in digital library systems that aggregate or exchange cultural heritage data can serve a number of useful functions. In this article, we present specific roles that collections can play in digital aggregations, representational requirements that arise from those roles, and modeling strategies for meeting the requirements. The functional roles of collections and collection descriptions speak to the needs of individual users accessing or contributing content, system developers seeking to improve search experiences, and institutions providing data to federated aggregations. However, the current data models that support cultural heritage aggregations are not designed to fully accommodate and integrate collection-level data. Therefore we have developed a set of general requirements for the representation of collections in digital aggregation systems. In order to demonstrate how these requirements can be addressed in a current operational context, we present specific strategies for collection representation in systems that use the Europeana Data Model.