My dissertation insists that Staten Island is central not only to the history of twentieth-century New York City, but to postwar urban planning and politics more broadly. Despite its absence from almost every major historical work on the postwar urban crisis, the borough was considered by many planners and politicians to be New York City's greatest asset and most volatile liability. Set against the rest of the boroughs' declining populations and shrinking tax revenues, Staten Island's large swaths of vacant acres provided a blank slate onto which urbanists mapped their conflicting critiques and cure-alls for the American city. Amongst a long list of influential politicians, environmentalists, and planning organizations that debated the future of Staten Island, Governor Nelson Rockefeller and the Regional Plan Association (RPA) stand out as having particular interest in and influence on the borough. My research at the Rockefeller Archive Center was integral to tracking and contextualizing both Rockefeller's and the RPA's planning approaches to the "forgotten borough" -- philosophies which by the early 1970s had come into tension with one another. While Rockefeller would move, in the late 1960s, toward encouraging a dense, socially-diverse, mass-transit oriented Staten Island, the RPA's uncompromising support of Gateway National Recreation Area would forestall precisely the type of new town planning project -- the South Richmond Development Corporation designed by James Rouse -- that was capable of densifying and integrating the borough's overwhelmingly white, middle-class southern shore.