Coincident with the first 75 years of City Planning education at MIT, the percentage of the world’s population living in urbanized areas has doubled. For the first time in human history, city dwellers now constitute the planet’s majority. With this fundamental change, the meanings of both “cities” and “planning” have been irrevocably altered. Cities, never separable from their hinterlands, are now even more inevitably recognized as city-regions. Planning, never solely about plan-making, is now even more wholly engaged with questions of process and implementation. Never simply a matter of physical form-making, planning is now thoroughly integrated with larger study of the social, economic, political, and cultural aspects of urban life. In this context, Changing Cities is both a description of the urbanization that has occurred, and a call to action.