Increased legal harmonization reinforces the need for a new way to test legal rules. As legal diversity decreases, there are fewer alternate rules to draw from, and thus potentially useful de facto experimentation with alternative rules becomes rarer and more difficult. This article argues that the ability to test legal rules in virtual worlds could help to solve a long-running, and worsening problem in the design of legal rules - the barriers to experimentation caused by an increasing tendency to the harmonization of law. In a world where real world experimentation with legal rules is likely to be useful, but also difficult and expensive, experimentation with legal rules in Virtual Worlds may be a valuable substitute. Large numbers of enthusiastic players in Virtual Worlds could test legal rules in an environment closer to the real world than many of the experiments that behavioral economists run to test economic behavior.