The correlation between social ties and political participation has been evident for some time, though very little attention is devoted to examining the causal mechanisms producing this relationship. This paper moves the literature in this direction by examining how an important feature of social networks -- levels of political expertise -- affect the attitudes underlying involvement. After outlining a model for explaining the relationship between social expertise and involvement, analysis of the 2000 American National Election Study shows that people who are in sophisticated social networks are less likely to be ambivalent about candidates and more likely to feel efficacious. This shows that social expertise supports participatory democracy by helping demystify politics, thus building up the reservoir of attitudinal resources necessary for involvement in politics.