In many empirical studies, ideology significantly predicts political outcomes, even after controlling for interests. This may reflect ideology’s influence on descriptive beliefs about the workings of the economic world. We investigate these beliefs about supply and demand theory, using survey methods and an experimental demonstration. As expected, relatively liberal respondents have more skeptical ex-ante beliefs (before viewing the experiment) about the theory. Surprisingly, however, relatively conservative respondents update beliefs (after viewing the experiment) so much less strongly that they have more skeptical ex-post beliefs. We explore and discount alternative explanations for these relationships between ideology and beliefs.