A model of extradyadic temptation and mate guarding was tested in the present dyadic daily report study. Results indicated that participants (perceivers) perceived their partner’s (targets) daily extradyadic temptation and that these perceptions predicted perceivers’ daily mate-guarding behaviors. Perceivers’ chronic jealousy moderated these relationships. These results suggest that perceivers, especially chronically jealous perceivers, are sensitive to their partners’ temptation for extradyadic relations and respond to this temptation with relationship-protective behaviors. Furthermore, perceivers’ mate-guarding behaviors predicted increases in targets’ subsequent daily commitment, suggesting that perceivers’ mate guarding works to deter targets from future infidelity by increasing targets’ commitment to the relationship. These findings suggest an interpersonal process in which people detect and then regulate their partners’ extradyadic temptation.