Firms increasingly use innovation tournaments to crowdsource innovation ideas from customers. This article uncovers antecedents and consequences of customers’ participation intensity over the course of a tournament. More specifically, the authors theorize on the effects that the type and timing of moderating feedback have on tournament participants’ participation intensity, as well as the effect of the latter on idea quality. Through two longitudinal experiments using a commercial innovation tournament platform, the authors show that moderating feedback stimulates ideators’ participation intensity. They find that negative feedback increases participation intensity, as compared to no feedback and positive feedback. Moreover, negative feedback, either provided in isolation or together with positive feedback, is more effective during the early stages than in the later stages of a tournament. Using a large-scale managerial survey, the authors show that higher participation intensity leads to higher idea quality and better business performance. The effect of participation intensity on idea quality is stronger than the effect of number of ideas and as strong as the effect of number of participants on idea quality.