For comments and feedback we thank Ana Arjona, Oriana Bandiera, Abhijit Banerjee, Eli Berman, Esther Duflo, Leopoldo Fergusson, Claudio Ferraz, Danilo Friere, Soeren Henn, Macartan Humphreys, Stephen Machin, Martin McGuire, Ted Miguel, Mushfiq Mobarak, Eduardo Montero, Daniel Ortega, Gerard Padró i Miquel, Paolo Pinotti, Bob Powell, Gérard Roland, Pieter Serneels, Jake Shapiro, Stergios Skaperdas, Tara Lyn Slough, Carlos Schmidt-Padilla, Rodrigo Soares, Maria Micaela Sviatschi, Lucia Tiscornia, Francesco Trebbi, Juan Vargas, Maarten Voors, Jeremy Weinstein, Austin Wright, participants at several seminars and conferences, and Raul Sánchez de la Sierra who was instrumental in conceptualizing the model. Innovations for Poverty Action coordinated all research activities. For research assistance we thank Bruno Aravena-Maguida, David Cerero, Peter Deffebach, Sebastián Hernández, Sofía Jaramillo, Juan F. Martínez, Juan Pablo Mesa-Mejía, Angie Mondragón, Helena Montoya, José Miguel Pascual, Andrés Preciado, María-Aránzazu Rodríguez-Uribe, Zachary Tausanovitch, Nelson Matta- Colorado and Martín Vanegas. We thank the Secretariat of Security of Medellín for their cooperation, especially the former Secretary of Security Andrés Tobón, as well as Lina Calle, Ana María Corpas and Andrés Machuca. For financial support, we thank the Centro de Estudios sobre Seguridad y Drogas (CESED) of Universidad de los Andes; the Peace and Recovery Program (P&R) at Innovations for Poverty Action (IPA); the PROANTIOQUIA foundation; The National Science Foundation (NSF); the UK Foreign, Commonwealth & Development Office trough the Crime and Violence Initiative at J-PAL; and the Economic Development and Institutions Programme (EDI) funded with UK aid from the UK Government, working in partnership with Oxford Policy Management Limited, University of Namur, Paris School of Economics and Aide á la Décision Économique. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.