The rati¯cation of ILO Labor Standards Conventions is a key explanatory variable in the empirical literature linking labor standards to economic performance. The assumption is that rati¯cation gives information on labor standards implemented in a country. This paper investigates the determinants of rati¯cation directly and, indirectly, the determinants of labor standards. We ¯nd considerable variation across di®erent 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 rati¯cation, legal systems do. Most interestingly, for some Conventions, even after controlling for basic economic characteristics and domestic legal institutions, we ¯nd that peer e®ects 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.