An auction is usually a process of buying and selling goods or services by offering them up for bid, taking bids, and then selling the item to the highest bidder or buying the item from the lowest bidder. Some exceptions to this definition exist and are described in the section about different types. The branch of economic theory dealing with auction types and participants' behavior in auctions is called auction theory.
The open ascending price auction is arguably the most common form of auction in use throughout history. Participants bid openly against one another, with each subsequent bid required to be higher than the previous bid. An auctioneer may announce prices, bidders may call out their bids themselves or have a proxy call out a bid on their behalf, or bids may be submitted electronically with the highest current bid publicly displayed.Auctions were and are applied for trade in diverse contexts. These contexts are antiques, paintings, rare collectibles, expensive wines, commodities, livestock, radio spectrum, used cars, online advertising, even emission trading and many more.