The DØ event data model (EDM) is a library of C++ classes and templates whose purpose is to support the implementation of reconstruction and analysis software. The central feature of the EDM is the event, a class that represents the results of a single beam crossing. The event acts as a container to manage all of the data associated with a single crossing: the raw output of the detector, the results of trigger processing, and the results of many different reconstruction tasks. Each of the items in this collection contains both the data describing the crossing in question as well as metadata that describe the configuration of the program that constructed these results. This allows us to run multi- ple instances of single algorithms with different configuration information (for example, several cone-based jet algorithms with different cone radii), and to distinguish between the output of these different algorithms. The EDM also provides a mechanism for access to the collec...