Bioregionalism is a philosophy that suggests that political, cultural, and economic systems are more sustainable and just if they are organized around naturally defined areas called bioregions, similar to ecoregions. Bioregions are defined through physical and environmental features, including watershed boundaries and soil and terrain characteristics. Bioregionalism stresses that the determination of a bioregion is also a cultural phenomenon, and emphasizes local populations, knowledge, and solutions.

Bioregionalism asserts "that a bioregion's environmental components (geography, climate, plant life, animal life, etc.) directly influence ways for human communities to act and interact with each other which are, in turn, optimal for those communities to thrive in their environment. As such, those ways to thrive in their totality—be they economic, cultural, spiritual, or political—will be distinctive in some capacity as being a product of their bioregional environment."

Bioregionalism is a concept that goes beyond national boundaries—an example is the concept of Cascadia, a region that is sometimes considered to consist of most of Oregon and Washington, the Alaska Panhandle, the far north of California and the West Coast of Canada, sometimes also including some or all of Idaho and western Montana. Another example of a bioregion, which does not cross national boundaries, but does overlap state lines, is the Ozarks, a bioregion also referred to as the Ozarks Plateau, which consists of southern Missouri, northwest Arkansas, the northeast corner of Oklahoma, southeast corner of Kansas.

Bioregions are not synonymous with ecoregions as defined by bodies such as the World Wildlife Fund or the Commission for Environmental Cooperation; the latter are scientifically based and focused on wildlife and vegetation. Bioregions, by contrast are human regions, informed by nature but with a social and political element. In this way bioregionalism is simply political localism with an ecological foundation.

Because it is a cultural idea, the description of a specific bioregion is drawn using information from not only the natural sciences but also many other sources. It is a geographic terrain and a terrain of consciousness. Anthropological studies, historical accounts, social developments, customs, traditions, and arts can all play a part. Bioregionalism utilizes them to accomplish three main goals:

1. restore and maintain local natural systems;
2. practice sustainable ways to satisfy basic human needs such as food, water, shelter, and materials; and
3. support the work of reinhabitation.

The latter is accomplished through proactive projects, employment and education, as well as by engaging in protests against the destruction of natural elements in a life-place.

Bioregional goals play out in a spectrum of different ways for different places. In North America, for example, restoring native prairie grasses is a basic ecosystem-rebuilding activity for reinhabitants of the Kansas Area Watershed Bioregion in the Midwest, whereas bringing back salmon runs has a high priority for Shasta Bioregion in northern California. Using geothermal and wind as a renewable energy source fits Cascadia Bioregion in the rainy Pacific Northwest. Less cloudy skies in the Southwest's sparsely vegetated Sonoran Desert Bioregion make direct solar energy a more plentiful alternative there. Education about local natural characteristics and conditions varies diversely from place to place, along with bioregionally significant social and political issues.

There is a strong affinity for bioregional thinking in many fields that relate to ecological sustainability.

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. They wanted to do "more than just save what's left" in regard to nature, wildness and the biosphere. During the 1970s, Planet Drum Foundation in San Francisco became a voice for this sentiment through its publications about applying place-based ideas to environmental practices, society, cultural expressions, philosophy, politics, and other subjects. By the late 70s, bioregional organizations such as the Frisco Bay Mussel Group in northern California and Ozark Area Community Congress on the Kansas-Missouri border were founded to articulate local economic, social, political, and cultural agendas. The Mussel Group eventually played a pivotal role in persuading the public to vote down a bioregionally lethal Peripheral Canal proposal to divert fresh water away from San Francisco Bay. The Ozarks group has held continuous annual gatherings to promote and support place-based activities. At present there are hundreds of similar groups (and publications) in North and South America, Europe, Japan, and Australia.

There is a strong affinity for bioregional thinking in many fields that relate to ecological sustainability. Restoration ecology practitioners readily grasp the importance of an appreciative local culture for their efforts to revive native plants and animals. Urban ecology advocates use bioregions for "nesting" their redesigned cities in a broad natural context. Permaculturalists and most organic farmers employ techniques that are appropriate to their particular locales and insist on maintaining soils, water sources, and native species. Poets, painters, theater groups, and other artists have embraced bioregional themes in their works. Grade school teachers introduce bioregional concepts, and graduate schools recognize theses and dissertations based on them. Followers of Deep Ecology claim bioregionalists as a social manifestation of their biocentric philosophy. Even traditional conservation and environmental groups including the Sierra Club have subsequent to the inception of bioregionalism adopted a system of"ecoregions" to address members' problems in home areas.

Bioregionalists are primarily concerned with their own local areas. There are a surprisingly large number of opportunities to address everyday living conditions for the benefit of local sustainability; as wide-ranging as resident-based reforestation projects in rural areas and community gardens in cities. Their influence is felt most strongly on county and city levels because this is where they take place and are most visible. Watershed-based organizations with bioregional priorities for basins as small as a creek or as large as the Great Lakes are a steadily growing phenomenon. Their recommendations to boards, councils, and other agencies aren't limited to creek restoration, water conservation, and other obvious issues, but may also include redrawing political borders to fit watershed lines and adopting ecological urban plans.