Traces the concept of ecosystem from its beginning, in Darwin's compelling images of "an entangled bank" of plants and animals living beside a river in a complex web of interdependence, to the present. Hagen pays special tribute to the British and American ecologists - Tansley, Frederic Clements, Charles Elton, G. Evelyn Hutchinson, Eugene and Howard Odum - whose research, debates, and students shaped the discipline over the course of a century.