This article seeks to explain cross-national differences on environmental behavior. After controlling for a series of sociodemographic and psychosocial factors, it was predicted that national levels of wealth, postmaterialism, education development, and environmental problems are positively related to environmental behavior. The national-level variance is to a substantial degree explained by individual-level variables, capturing compositional effects. The remaining variance is explained by the contextual-level variables. All of the country-level variables are predictors in the expected direction, with the exception of environmental degradation, which is negatively related to behavior, and education development, which has no impact on private environmental behavior. More importantly, cross-level interactions show that in more developed countries, there are stronger relationships between proecological attitudes and reported proenvironmental behavior. These findings contribute to the growing cross-cultural research on environmental behavior pointing out the necessity of simultaneously assessing the effects of both individual and contextual-level forces affecting behavior across nations.