This article explores the theory and practice of society's participation in strengthening government accountability. It argues that both "exit" solutions based in marketization and "voice" solutions grounded in "coproduction," social protest or consultation are insufficient. The best way to tap into the energy of society is through "co-governance," which involves inviting social actors to participate in the core activities of the state. By way of demonstration, the article examines case studies from a wide range of contexts (Brazil, Mexico, the United States, India) and policy areas (poverty reduction, infrastructure provision, school reform, electoral administration, police reform). (C) 2003 Elsevier Ltd. All rights reserved.