Mountain regions are uniquely sensitive to changes in climate, and are especially vulnerable to climate effects acting on many biotic systems and the physical settings. Because mountain regions serve as sources of needed natural resources (e.g., water, forests) and as foundations for desired human activities (e.g., tourism, places to live), changes in mountain systems cascade into issues of regional and national concern. Mountains also comprise highly sensitive systems that may act as canaries in the coal mine to provide early signals of significant climate-driven changes in many of our valued resources. Why the Focus on the Western United States?. The Mountain Climate Science Symposium, held last May, arose from the recognition by a cross section of physical scientists working on western United States mountain climate and ecosystems that there is need for more and improved observations, better integration, and greater attention at all levels of society to potential vulnerability of western society to climate variability and change. An ad hoc committee was formed to promote greater understanding of the physical processes affecting western mountains and to promote better communication of scientific findings to decision makers. The group's goal is to establish a Consortium for Integrating Climate Research in Western Mountains (CIRMOUNT), and the symposium was organized to facilitate that goal.