An auction is a sale that offers items up for bid. The items can be anything from valuable art, house estates, sports items, etc. A person or business puts an item(s) up for auction, and the person or company who bids the highest amount of money, wins the item(s).

There are various types of auctions including the English auction where participants bid openly against one another. The winnter is the person who ends with the highest bid. The Dutch auction opens with an auctioneer asking for a high price and lowering the price until a bidder accepts the price or a predetermined minimum amount is reached. A Sealed First-Price auction allows bidders to submit bids in a sealed envelope. The highest bid openned bins the item. A Silent is a sealed variant often used in charity events, but involvesthe simultaneous sale of multiple items.The highest bidder pays the price they submitted for a certain item. A Procurement auction: reverses the roles of seller and buyer. The buyer puts out an RFQ for a given commodity and providers offer progressively lower prices in hopes of getting procuring an item. At the end of the auction, the lowest bid wins. Open Outcry auctions are exciting and used in stock exchanges and commodity exchanges, where trading occurs on a trading floor and traders may enter verbal bids and offers simultaneously. This type of auction is being replaced by electronic trading platforms.

The world's three largest auction houses are Christie's, Sotheby's and Bonhams. The world's largest online auction site is eBay.