In this chapter, we study all-pay auctions. As in the auction formats we examined in previous chapters, every bidder submits his bid and the bidder submitting the highest bid wins the object. However, as opposed to other auctions where only the winning bidder must pay for the object (either the highest or second-highest bid), in the all-pay auction every bidder must pay the bid that he submitted. As expected, this makes bidders less aggressive in their bids than in other auction formats, which we demonstrate to hold under different settings. Examples of all-pay auctions include contests, political campaigns, awarding of monopoly licenses, and R&D races where players (e.g., firms) cannot recover their participation costs upon losing. More recently, we can also find this type of auctions being used by internet sellers such as QuiBids.com , which requires bidders to purchase tokens/points before an auction starts, and then submit their token bids, which cannot be recovered regardless of the outcome of the auction.