In December 1987, the United States Congress enacted Public Law (P.L.) 100-223, which requires the administrator of the Federal Aviation Administration (FAA) to complete the development of the Traffic Alert and Collision Avoidance System (TCAS II) and ensure that it is installed on all airplanes with more than 30 passenger seats by December 1991. To implement the provisions of this legislation, the FAA issued the TCAS Rule in January 1989, which mandates that airline aircraft with more than 30 seats be equipped with TCAS II avionics no later than December 31, 1991.Both before and after the Rule was issued, concern was expressed regarding the effect that large-scale implementation of TCAS would have on the air traffic control (ATC) system, the proposed compliance schedule, and the impact that such a schedule would have on the airlines and the avionics manufacturers. In response to these concerns, P.L. 101-236, which supersedes P.L. 100-223, establishes the equipage schedule and provides the FAA with the mandate to conduct an operational evaluation of TCAS II avionics within the National Airspace System (NAS). This evaluation has been designated the TCAS Transition Program (TTP).This paper discusses the objectives of the TTP, participants and responsibilities, key technical issues, program milestones, and required resources. The TTP will build on the foundation of operational experience developed during past evaluations (Piedmont Phase II, Northwest Airlines, and the United Airlines Limited Installation Program [LIP]) to evaluate the operational acceptability of TCAS II and ensure its safe integration within the NAS when installed and operated on a large number of commercial aircraft.