Traffic Theory describes and illustrates the key models of traffic flow and associated traffic phenomena such as conflicts in traffic, traffic generation and assignment, and traffic control. The use of these various models are explored both in terms of how they have improved traffic systems over the years and how better implementation of these models can accelerate the successful deployment of Intelligent Transportation Systems (ITS). Furthermore, the book outlines opportunities for development of additional models needed for continued improvement of ITS.The book is intended as a textbook for a college Transportation Science curriculum, and as a reference book for researchers in Transportation Science. Dr. Gazis has concentrated in the book's presentation on the fundamental concepts and methods in the various areas of traffic theory.