A recognized systems engineering best practice is early development of operational concepts during system development and documentation of those operational concepts in one or more operational concept documents. Recognizing this best practice, U. S. Department of Defense (DoD) and NASA standard procedures have required that information relating to system operational concepts is prepared in support of the specification and development of systems. In the past, the DoD has published Data Item Descriptions (DIDs), and NASA has published Data Requirements Documents (DRDs), which describe the format and content of the information to be provided.This AIAA Guide describes which types of information are most relevant, their purpose, and who should participate in the operational concept development effort. It also provides advice regarding effective procedures for generation of the information and how to document it.