Addressing environmental problems caused by solid waste generation requires household separation of waste as well as general waste reduction. The factors that influence waste separation behavior are context specific, and much of the research on waste separation has been centered in Western countries that tend to emphasize individualism over collectivism. We apply the theory of planned behavior to explain household waste separation behaviors among households in Mashhad, Iran, and we also build on this theory by incorporating structural situational factors in our analysis. We use structural equation modelling to analyze survey results from 970 households and find support for the theory of planned behavior. In particular, subjective norms were a stronger predictor of behavioral intentions and waste separation behavior, which may be reflective of Iran’s stronger emphasis on collectivism compared to Western countries. Structural factors were negatively associated with waste separation. In Iran and similar contexts, recycling policies that appeal to local norms may have increased success, especially when coupled with decreased barriers to waste separation such as facility siting.