Environmentalism involves hundreds of international environmental groups, thousands of national groups, and tens of thousands of local ones. It also includes hundreds of international agreements, hundreds of national environmental agencies, and countless environmental sections in other organizations from those in multinational corporations to ones in regional and international organizations. Such environmental concepts as sustainable development, the precautionary principle, corporate social responsibility, and eco-labeling percolate from all of these sources. Every year, new ideas, refinements, policies, institutions, markets, and problems continue to enter into environmental debates and discourses, making it nearly impossible to keep abreast of the changes constantly taking place. With this constant shifting landscape in mind, the Historical Dictionary of Environmentalism strategically skips across issues, concepts, time, organizations, and cultures, not with any pretense of producing a definitive dictionary but rather with the aim of producing an inclusive, wide-ranging, and global history of environmentalism. This goal is accomplished through a chronology, a list of acronyms and abbreviations, an introductory essay, and over 300 cross-referenced dictionary entries.