During the fall of 2001, a Cooperative Research Agreement between the U.S. Environmental Protection Agency and MCNC began a Community Modeling and Analysis System (CMAS) center. The CMAS will foster development, distribution, and use of the Models-3/CMAQ (Community Multiscale Air Quality) air quality modeling system. The CMAS is hosted by MCNCs Environmental Modeling Center in Research Triangle Park, North Carolina. The objectives of the CMAS are to (1) serve as a bridge between members of the Models-3/CMAQ modeling community, (2) encourage the growth of the user community, (3) serve as an information clearinghouse for model applications, emission modeling methods and data, (4) provide education about the models and their uses, (5) maximize the scientific content and performance value of the Models-3/CMAQ system by encouraging the expansion of the contributing developer community and taking advantage of multiple incremental contributions, and (6) provide computer and skill resources to the Models-3/CMAQ modeling community benefitting from economies of scale. Support and development work includes both emission modeling (through the Sparse Matrix Operator Kernel Emission system) and the CMAQ chemistry-transport modeling components. As a community modeling support center, the CMAS is open to all interested participants. The center is organized into five functional parts: (1) Administration, (2) Outreach, (3) Application Support, (4) Software Development, and (5) Modeling Research. The model code accepted and released as a part of Models-3/CMAQ will be open and shared with all. The External Advisory Committee, governing the CMAS policies and priorities, is a technically knowledgeable group including representatives of state and regional agencies, EPA, industry, consultants, academic institutions, and foreign users.