Under the guidance of a steering committee of public- and private-sector representatives from the Canadian transportation industry, the development of the Canadian Intelligent Transportation System (ITS) Architecture was initiated in August 1999. In general, the Canadian effort subsumes all of the U.S. National ITS Architecture work and extends and modifies it to provide new services and areas of coverage and to reflect differences between the nations and the existence of new and different stakeholders. Since there is much commonality between the technical definitions of the two architectures, it is important to understand the explicit relationships. The development of the Canadian ITS Architecture is examined, and the differences between the architectures of the United States and Canada are illustrated. The development included an extensive review of other relevant ITS architecture and standards initiatives. On the basis of the review and significant ITS stakeholder input, an initial draft ITS architecture framework was developed that defined the user services, user subservices, and market packages applicable to Canada. After a review by ITS stakeholders, the revised ITS architecture framework was used to develop definitions of both the physical and the logical architectures of the Canadian ITS Architecture. The follow-up support activities anticipated for the Canadian ITS Architecture are reviewed, and the potential for iterative development with the U.S. National ITS Architecture is examined.