Today, the majority of the world lives in housing that is not designed by architects, in neighborhoods that were not planned, and in cities that do not comply with urban regulations. Today, urban informality is majoritarian. This fact disproves urban planning, haunts architecture, hypnotizes anthropology, and eludes economics. Without a better understanding of urban informality, designers, entrepreneurs, policy makers, and thinkers are trapped in either romantic or victimizing traditional narratives. However, ideas about informality have evolved much from the moment when the concept was first introduced by an anthropologist into the development economics discourse 50 years ago. Now we know that informality can be measured, that it is not synonymous with poverty, and that it does not go away with economic growth. Using official statistics, the International Labor Organization reports 61.5% of the world’s employment is informal, which means that working informally is the norm both in developing countries in the South as well as developed ones in the North. Understanding better urban informality is nothing less than a moral imperative for designers, scholars, urbanists, activists, and policymakers, who need to ensure that their well-intended initiatives do not have foreseeable contradictory consequences. Moreover, a better understanding of urban informality is an exciting opportunity to produce truly innovative designs and ideas. This seminar invites students to understand informality by disentangling current debates between architects and social scientists, as well as those within economics. Underlying questions of this course are: What does the persistence of urban informality tell us about development, society, and the economy at large? How can designers and thinkers use a better understanding of informality to guide better professional practices and non-ideologized approaches?