We examine the associations between personality traits and the strength and direction of partisan identification using a large national sample. We theorize that the relationships between Big Five personality traits and which party a person affiliates with should mirror those between the Big Five and ideology, which we find to be the case. This suggests that the associations between the Big Five and the direction of partisan identification are largely mediated by ideology. Our more novel finding is that personality traits substantially affect whether individuals affiliate with any party as well as the strength of those affiliations, effects that we theorize stem from affective and cognitive benefits of affiliation. In particular, we find that three personality traits (Extraversion, Agreeableness, and Openness) predict strength of partisan identification (p < 0.05). This result holds even after controlling for ideology and a variety of issue positions. These findings contribute to our understanding of the psychological antecedents of partisan identification.