"We examine the characteristics and the relative strength of third party sanctions in a series of experiments. We hypothesize that egalitarian distribution norms and cooperation norms apply in our experiments, and that third parties, whose economic payoff is unaffected by the norm violation, may be willing to enforce these norms although the enforcement is costly for them. Almost two-thirds of the third parties indeed punish the violation of the distribution norm and their punishment increases the more the norm is violated. Likewise, up to roughly 60 percent of the third parties punish the violation of the cooperation norm. Thus, our results show that the notion of strong reciprocity also extends to the sanctioning behavior of "unaffected" third parties. In addition, these experiments suggest that third party punishment games are powerful tools for studying the characteristics and the content of social norms. Further experiments indicate that second parties, whose economic payoff is reduced by the norm violation, punish the violation much more strongly than do third parties. We also collect questionnaire evidence that is consistent with the view that fairness motives and negative emotions are a determinant of third party sanctions."