Nonformal urbanization will be the dominant mode of urban growth in the coming decades. The results of this growth go by many well-known names, including: slums, favelas, and shantytowns. The precarious conditions of these settlements, excluded from formal legal, social, and infrastructural systems, present a central challenge-and opportunity-in our current and future cities. Short texts explain a range of projects and initiatives, complimented by photographs and personal insights, to present a diversity of responses to the global phenomenon known here as "Metropolis Nonformal."