An empirically rich reconstruction of how informality became an intrinsic part of urban life across three continents. Over a quarter of the world’s urban population lives in informal settlements. While informality as a concept has been widely debated, we still know very little about the phenomenon’s urban history or how that history has shaped the evolution of world cities. Spotlighting the historical processes that have created and sustained urban informality for more than a century, editors Charlotte Vorms and Brodwyn Fischer and this volume’s contributors reveal informality as an intrinsic feature of urbanity, shaping not only cities across the globe but also deeper processes of state formation, socioeconomic stratification, and political struggle.   The volume brings together case studies spanning more than a hundred years, drawn from Latin America (Brazil, Chile, Venezuela, and Mexico), Northern Africa (Morocco and Algeria), and Latin Europe (France, Spain, and Italy). Together, they show that informality is neither a contemporary crisis nor a predicament unique to the Global South. Topics include the origins of informal settlements and their relationship with law and institutional power; grassroots efforts to legitimize shantytown communities; mass social movements for rights to the city; the role that shantytown removal campaigns played in populist politics, fascism, and colonialism; and the ways that informality perpetuated racial and ethnic inequalities. Informal Cities is an indispensable guide to the complex and fraught terrain of urban informality in its many historical guises.