Compulsory rules are known to have far-reaching effects beyond boosting electoral participation rates. This article examines the relationship between compulsory voting and partisan attachments. A theory of attachment formation and strength is engaged that argues that compulsory voting boosts the likelihood that one will identify with a party and, in turn, the strength of party attachments among identifiers. The statistical model accounts for both the hierarchical structure of the data (individuals in elections) and the dual nature of the dependent variable (individuals report a strength of attachment only for the party with which they identify). Using data from the Comparative Study of Electoral Systems, it is demonstrated that compulsory voting does indeed increase both the incidence and the strength of partisanship.