This paper, forthcoming in *Journal of Economic Surveys*, provides a non-technical survey of auction theory, introducing and describing key papers in the field. It begins with fundamental concepts and then delves into the analysis of optimal auctions, the revenue equivalence theorem, and marginal revenues. The paper addresses various topics such as risk-aversion, affiliation, asymmetries, entry costs, collusion, multi-unit auctions, double auctions, royalties, incentive contracts, and other advanced topics. The most important papers are reproduced in a companion book, *The Economic Theory of Auctions*. The paper highlights the importance of auction theory for practical, empirical, and theoretical reasons. It is widely used in economic transactions, from government auctions to private sales, and serves as a testing ground for economic theory, especially game theory with incomplete information. The theory has also been crucial in understanding other methods of price formation, such as posted prices and negotiations. The paper covers four basic types of auctions: ascending-bid, descending-bid, first-price sealed-bid, and second-price sealed-bid auctions. It discusses the basic models of auctions, including private-value and common-value models, and the bidding strategies in these auctions. The revenue equivalence theorem, which states that different auction mechanisms yield the same expected revenue under certain conditions, is a fundamental result in auction theory. The paper also explores the effects of relaxing assumptions, such as risk-aversion, correlation or affiliation of bidders' information, and asymmetries. It examines the impact of entry costs and the number of bidders on auction outcomes. The paper concludes with a discussion on testing the theory and provides technical details, numerical examples, and bibliographies.This paper, forthcoming in *Journal of Economic Surveys*, provides a non-technical survey of auction theory, introducing and describing key papers in the field. It begins with fundamental concepts and then delves into the analysis of optimal auctions, the revenue equivalence theorem, and marginal revenues. The paper addresses various topics such as risk-aversion, affiliation, asymmetries, entry costs, collusion, multi-unit auctions, double auctions, royalties, incentive contracts, and other advanced topics. The most important papers are reproduced in a companion book, *The Economic Theory of Auctions*. The paper highlights the importance of auction theory for practical, empirical, and theoretical reasons. It is widely used in economic transactions, from government auctions to private sales, and serves as a testing ground for economic theory, especially game theory with incomplete information. The theory has also been crucial in understanding other methods of price formation, such as posted prices and negotiations. The paper covers four basic types of auctions: ascending-bid, descending-bid, first-price sealed-bid, and second-price sealed-bid auctions. It discusses the basic models of auctions, including private-value and common-value models, and the bidding strategies in these auctions. The revenue equivalence theorem, which states that different auction mechanisms yield the same expected revenue under certain conditions, is a fundamental result in auction theory. The paper also explores the effects of relaxing assumptions, such as risk-aversion, correlation or affiliation of bidders' information, and asymmetries. It examines the impact of entry costs and the number of bidders on auction outcomes. The paper concludes with a discussion on testing the theory and provides technical details, numerical examples, and bibliographies.