This article describes and discusses the results of two comparative studies of prostitution policy in Europe that are complementary in their design and methodology. One is a comparison of 21 countries using a most different systems design; the other an in-depth comparison of Austria and The Netherlands, using a most similar systems design. The two studies found a remarkable continuity in the inherent approach to the regulation of prostitution and its effects. Despite differences in political regime, administrative organization, and national cultures, since the middle of the 19th century, the purpose of prostitution policy has been to impose strict controls on sex workers and to a lesser extent their work sites. The effects of this approach have been disappointing: despite rhetorical claims to the contrary the control of sex workers has no discernable effect on the prevalence of prostitution in society. The effects of policies aimed at control are mostly negative in that they corrode the human and labor rights of sex workers. The article discusses several challenges to the regulation of prostitution (such as its deeply moral nature and the lack of precise and reliable data) as well a number of other important outcomes (such as the importance of local policy implementation for the effects of regulation). The article concludes with the empirically substantiated suggestion that a form of collaborative governance in which sex worker advocacy organizations participate in the design and implementation of prostitution policy offers real prospects for an effective and humane prostitution policy.