This essay was presented as a lecture by Thoreau in his later years, but only published after his death. It's best known for its quote "In wildness is the preservation of the world", which has become a rallying cry of the environmental movement. But Thoreau means much more by the phrase then most of his modern admirers realise. "Wildness" is Nature itself, and humankind is seen as an aspect or manifestation of Nature; the rules that apply to one apply to the other.