Research indicates that if third parties provide assistance to sanctioned states, the sanctions are less likely to be successful. However, the scholarship on the profile of sanctions busters and their motivations remains underdeveloped. Drawing on the realist and liberal paradigms, this piece develops two competing theories to account for third-party sanctions-busting. The hypotheses drawn from these theories build upon existing work on sanctions, the political determinants of international trade, and the effects of indirect interstate relationships. A quantitative analysis develops a new measure to identify sanctions-busting behavior for a dataset covering 77 sanctions cases from 1950 to 1990. The liberal and realist explanations are then tested. The results offer strong support for the liberal theory of sanctions-busting and less support for the realist theory. In particular, the analysis reveals a counter-intuitive finding that a sender’s close allies are more likely to sanctions-bust on the target’s behalf than are other states.