PM TRADE and DARPA have funded the University of Central Florida Institute for Simulation and Training (UCF/IST) to develop a Draft Standard for the Interoperability of Defense Simulations at the protocol data unit level. The second draft of the standard was completed in February 1991. The consensus of government and industry opinion was that the document represented a major step forward toward interoperability of dissimilar simulations. Based on inputs from government, industry and academia at four workshops, IST has developed a final draft standard for submittal as a DoD standard. This paper presents the contents of this standard, its intended use and its anticipated impact on the simulation and training industry. Discussion of the standard's contents include the protocol data units, their intended use and the underlying communications architecture. The paper also addresses future revisions of the standard and the attendant expanded capabilities.