The outcome of a mechanism is, from the perspective of an agent, uncertain ex-ante since the other agents’ types are unknown or the mechanism itself randomizes over outcomes. Most work on mechanism design assumes that agents maximize their expected utility when faced with uncertainty. There is, however, strong empirical evidence that expected utility theory does not explain agents’ behavior in common mechanism design settings well. This workshop aims to promote a more general theory for mechanism design without the expected utility hypothesis by combining the expertise on decision-making under uncertainty in the decision theory community with methods from mechanism design.