The environmental movement in the United States has undergone substantial changes during the last century. From its approximate beginnings in the conservation movement toward the end of the 19th century, the movement has evolved from a relatively narrow preoccupation with the conservation of local resources and the preservation of scenic areas, parks and forests to the broader concerns of toxic pollution, biodiversity protection and the prevention of global climate change. Early organisations and activists were primarily conservationists and preservationists. While conservation and preservation still exist within the movement, the organisations, activists and ideologies of the movement have expanded to encompass a framework more adequately depicted as ‘environmentalist’ or even ‘ecologist’. This paper provides a broad outline of how the American environmental movement has evolved and how, in doing so, it has responded to the evolving social context in which it exists.