This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. The book presents William Wordsworth's and Ralph Waldo Emerson's work inspired early environmentalists such as Octavia Hill and John Muir, who emerged toward the end of the nineteenth century to defend the trees and open space. Early environmentalism refers to a host of literary and nonliterary antecedents that motivate the premodern environmental movement in the 1890s. The book compares, The Naturalist's Summer-Evening Walk, a short poem from White's Natural History, with Wordsworth's An Evening Walk to show reciprocity: the naturalist-turned-poet and also poet-turned-naturalist. It gives an analysis of Wordsworth's green letters in 1844 and Emerson's green lectures from 1841-1844. The book concentrates on the open space movement in England. It delineates continuity between Wordsworth and Hill leading to the National Trust in England. It also hinges on identifying evidence of Romantic naturalism within Muir's writing.