Data link interfaces are a very important part of the heavy duty vehicle industry; sharing information between subsystems is vital. SAE Recommended Practices J1708, J1587 and J1922 were developed to provide standards for proprietary communications, general information sharing, diagnostic definition and early powertrain controls. The industry realized, however, that these standards would not accomplish the ultimate goal-that of a high speed control and communications network. The development of more capable serial data communications for the heavy duty vehicle industry was prompted by the following: the desire of component suppliers to integrate subsystems for improved performance; the advancement of technology; customer expectations; and government regulations. Therefore, the Truck and Bus Control and Communications Network Subcommittee began development of SAE Recommended Practice J1939 even as the J1708, J1587 and J1922 standards were being completed-this new standard would enhance previous capabilities and add new ones to better support controls and multiplexing on a single network. This paper presents the serial data communications adopted in the draft J1939 documents by discussing three major areas: the definition of J1939, the supporting information which helped determine why J1939 is like it is, and the advantages of a J1939 network.