The ratification of ILO Labor Standards Conventions is a key explanatory variable in the empirical literature linking labor standards to economic performance. The assumption is that ratification gives information on labor standards implemented in a country. This paper investigates the determinants of ratification directly and, indirectly, the determinants of labor standards. We find considerable variation across different Conventions, and across developing and developed countries. But there are some systematic and interesting patterns. While economic variables such as real per capita income do not explain ratification, legal systems do. Most interestingly, for some Conventions, even after controlling for basic economic characteristics and domestic legal institutions, we find that peer effects are in play - the probability of adopting an international standard depends on how many other countries in a peer group have already adopted that standard.