Although the decision to engage in prosocial behavior has received research attention, the literature offers a limited understanding of fairness and uncertainty as antecedents. We propose that one can encourage prosocial decision making simply by invoking the notion of fairness because of its effects on the perceived trustworthiness of the invoking party. We also elucidate the complex role of uncertainty in prosocial decisions in that it has a negative effect while also serving to strengthen the positive effect of fairness salience. Our ideas are tested in two prosocial decision contexts, including participative pricing (i.e., “pay what you want”) and charitable giving. Data from an archival study of a naturally occurring event and two controlled experiments offer support for our arguments. Copyright © 2016 John Wiley & Sons, Ltd.