The Traffic Alert and Collision Avoidance System (TCAS) is a beanon-based airborne collision avoidance system that is able to operate in all airspace without reliance on ground equipment. The TCAS concept encompasses a range of capabilities that include TCAS I, a low-cost, limited-perofrmance version, and TCAS II, which is intended to provide a comprehensive level of separation assurance in all current and predicted airspace environments through the end of this century. This document provides a functional overview of the TCAS II including operating features, a description of the avionics package, and examples of surveillance data obtained with experimental TCAS equipment.