Are judgments written by professional judges more likely to elicit compliance? I exploit exogenous variation in the composition of European Court of Human Rights (ECtHR) chambers to evaluate this question. I find that judgments written by panels with a relatively high proportion of career judges are more likely to be implemented quickly than are judgments that come from panels with high proportions of former academics, legal diplomats, politicians, or private practitioners. This suggests that the performance of international courts could be improved by changing their professional composition. Theoretically, it implies that compliance is not merely a function of political incentives but also of the characteristics of those who interpret international law. Professional judges are both important compliance constituencies and consumers of legal reasoning. I build on sociological theories of the legal profession to explain why professional judges may be more amenable to judgments written by other professional judges.