An auction is a process of buying and selling goods or services by offering them up for bid, taking bids, and then selling the item to the winning bidder. In economic theory, an auction may refer to any mechanism or set of trading rules for exchange.

There are several variations on the basic auction form, including time limits, minimum or maximum limits on bid prices, and special rules for determining the winning bidder(s) and sale price(s). Participants in an auction may or may not know the identities or actions of other participants. Depending on the auction, bidders may participate in person or remotely through a variety of means, including telephone and the internet. The seller usually pays a commission to the auctioneer or auction company based on a percentage of the final sale price.