Communities are increasingly defining 'health' for themselves, then becoming the main actors in actions to improve their health and well being. These community members work from a broad and inclusive definition of 'health' that often incorporates environmental health as a key aspect. They also assume an ecological, or systems, viewpoint that integrates many aspects of the community that affect health and well being, including housing, health, economy, education, transportation, youth and family issues, as well as health and illness care. This paper describes a program that involves 28 large and small, urban and rural communities in the United States state of Colorado that undertook this type of community-based health improvement project. The Colorado Healthy Communities Initiative (CHCI) was designed to bring together citizens in Colorado to work collaboratively to make their communities healthier. This paper describes the program's background, including its principles, processes, and participants, then focuses on the particular aspects of environmental health that communities included in their definitions of a 'healthy community'.