This study explored the association between sociosexuality (behavior, attitudes, and desire) and commitment to understand sexual infidelity in current relationships. We also explored how these variables were associated with attitudes toward infidelity. Participants were romantically involved heterosexuals (N = 252; 51 women, 201 men; M_age = 41.13, SD = 9.82) registered on a dating Web site directed at romantically involved individuals. Results showed that sociosexuality, alongside commitment, was associated with sexual infidelity. Individuals who had (versus had not) previously engaged in infidelity reported more unrestricted sociosexuality, while reporting less commitment. For individuals reporting prior sexual infidelity, unrestricted sociosexual desire and lesser commitment were associated with more permissive perceptions of infidelity. For individuals reporting no prior sexual infidelity, greater commitment was always associated with more strict perceptions of infidelity. No gender differences emerged in the analyses. Also, no differences were found according to individual motivations (i.e., looking to know other people versus seeking casual sex) or relational motivations (i.e., individual registration versus registration as a couple) underlying individuals’ registration on the Web site. These results are an important addition to the literature on infidelity by analyzing a specific sample motivated to engage in infidelity. Implications for future research are discussed.