Psychological contract fulfillment—an individual’s perception of the degree to which an organization fulfills its promises—is critical to understand how people behave in exchange relationships. I examine if fulfillment explains exit, (aggressive and considerate) voice, loyalty, and neglect behaviors of volunteers. Moreover, I test whether these relationships are mediated by violation and trust. Data were collected from 215 volunteers using an online survey and analyzed using structural equation modeling. Results indicated that fulfillment related negatively to exit, aggressive voice, and neglect behavior and positively to considerate voice behavior. Mediation analyses confirmed that violation and trust acted as mediators. I conclude that fulfillment is critical to understand why volunteers display exit, (aggressive and considerate) voice, and neglect behavior. Moreover, I propose that violation and trust are able to explain how fulfillment is related to these behaviors, through a “hot” and “cool” response system, respectively.