MAINSTREAM, GRASSROOTS, and radical environmental groups operate very differently from one another. Mainstream groups work within the prevailing legal and political systems at the national level, influencing lawmakers, government officials, and the public to create new environmental laws, policies, and practices. Grassroots groups work at the local level to address specific environmental problems, using tactics similar to those of mainstream environmentalists. Radical groups work against the prevailing legal and political systems, often flouting the law and the government to fight what they call "anti-environmentalism."

Buying land

One of the primary goals of mainstream environmental groups is to maintain biodiversity, or the existing variety of biological species on Earth. Therefore they work to preserve wildlife habitats and support research on endangered plants and animals.

The main tactic that mainstream environmental groups use to protect a piece of...