The issue of prostitution is an abiding and current concern for which public policies have differed over time and across countries. Today’s debates bring into opposition two ethical positions—dignity versus freedom—between groups that are in some way affected by regulations on prostitution. This article addresses the legislation on prostitution and asks which legal solutions prove most effective in lowering the harmful effects of prostitution. After recalling the theoretical framework of the New Institutional Economics (Williamson, 1975, 1985, 1994), we make a comparative analysis of modes of governance of transactions in the field of prostitution services. The article concludes with a few comments on the transaction of other legal or illegal goods or services such as alcohol, cigarettes, and drugs.