A growing body of literature argues that democracies are more likely to comply with international agreements than authoritarian states. However, substantial variation exists in the compliance behaviour of democracies. How can this variation be explained? The same mechanism that links regime type to compliance, namely electoral competition, also explains variation in compliance amongst democracies. This is because the nature of electoral competition varies across democratic electoral systems. An analysis of democratic GATT/WTO member countries from 1980 to 2003 reveals that countries with majoritarian electoral rules and/or single-member districts are more likely to violate GATT/WTO rules than those with proportional electoral rules and/or multi-member districts.