How do the members of societies that can’t use government or simple ostracism produce social order? To investigate this question, Peter Leeson uses economics to analyze Gypsy law. Gypsy law leverages superstition to enforce desirable conduct in Gypsy societies where government is unavailable and simple ostracism is ineffective. According to Gypsy law, unguarded contact with the lower half of the human body is ritually polluting, ritual defilement is physically contagious, and non-Gypsies are in an extreme state of such defilement. These superstitions repair holes in simple ostracism among Gypsies, enabling them to secure social cooperation without government. Gypsies’ belief system is an efficient institutional response to the constraints they face on their choice of mechanisms of social control.