This chapter reviews the historical context of scenarios, beginning with brief sketches of early scenario activity, from its post-World War II origins up to about a decade ago. It focuses in particular on the subset of environmental global scenario projects that have a public policy and scientific orientation, since these are of greatest interest to the Millennium Ecosystem Assessment. Special consideration is given to the following post-1995 global scenario building exercises: Global Scenarios Group, Global Environment Outlook, Special Report on Emissions Scenarios, World Business Council for Sustainable Development, World Water Vision, and the Organisation for Economic Co-operation and Development. These scenarios, despite their diversity, are rooted in a common set of archetypal visions of the future: evolution, progression, and decline.