The concept of Cascadian bioregionalism is closely identified with the environmental movement. In the early 1970s, the contemporary vision of bioregionalism began to be formed through collaboration between natural scientists, social and environmental activists, artists and writers, community leaders, and back-to-the-landers who worked directly with natural resources. A bioregion is defined in terms of the unique overall pattern of natural characteristics that are found in a specific place. The main features are generally obvious throughout a continuous geographic terrain and include a particular climate, local aspects of seasons, landforms, watersheds, soils, and native plants and animals. People are also counted as an integral aspect of a locale's life, as can be seen in the ecologically adaptive cultures of early inhabitants, and in the activities of present-day reinhabitants who attempt to harmonize in a sustainable way with the place where they live.

A bioregion is an ecologically and geographically defined area that is smaller than a biogeographic realm, but larger than an ecoregion or an ecosystem, and is defined along watershed and hydrological boundaries. People are counted as an integral part of the definition of a bioregion.