An atlas of urban informality, taking the favelas in Brasil as a case study: In Rio de Janeiro over 1 million people live in so-called favelas. Often described as informal, favelas and other unregulated urban conditions have in many cities become the rule, rather than the exception. Informal urbanism is a paradigm that is fast becoming the defining characteristic of 21st century urban life. It organizes not just housing, but also infrastructures, geographies, economies, and politics. But what exactly makes a city informal? How do favelas and informality propose a new model for understanding the contemporary city? 100% Favela brings together, for the first time in translation, Brazil's leading architects, urbanists, photographers, and economists to discuss, map, and interpret the informal city in its myriad forms.