Simplifying entry regulation has been a popular reform since the publication of Djankov and others (2002). The inclusion of business entry indicators in the World Bank's Doing Business project has led to an acceleration in reform: in 2003–08, 193 reforms took place in 116 countries. A large academic literature has followed: 201 academic articles have used the data compiled by Djankov and others (2002) and subsequently by the World Bank. The author identifies three theories as to why some countries impose burdensome entry requirements. He also surveys the literature on the effects of making business entry easier.