We consider auctions for a single indivisible object, in the case where the bidders have information about each other which is not available to the seller. We show that the seller can use this information to his own benefit, and we completely characterize the environments in which a well chosen auction gives him the same expected payoff as that obtainable were he able to sell the object with full information about each bidder's willingness to pay. We provide this characterization for auctions in which the bidders have dominant strategies, and for those where the relevant equilibrium concept is Bayesian Nash. In both setups , the existence of these auctions hinges on the possibility of constructing lotteries with the correct properties.

This paper deals with the optimal design of resource allocation mechanisms in the presence of asymmetric information. A buyer's valuation function is allowed to depend on the characteristics of other buyers as well as his own and sufficient conditions are provided under which the seller can extract the full surplus from the buyers in an "ex post Nash" equilibrium. The result is then applied to the important problem of optimal auction design.

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We study the`backbone market' in the Internet. After discussing the structure of the Internet, we use an extension of the Katz-Shapiro network model to analyze the strategies that would be used by dominant backbone. We show that a larger backbone prefers a lower quality interconnection than the smaller one. We then analyze à targeted degradation' strategy where the larger backbone lowers the quality of interconnection to its smaller rivals in turn. Finally, we show that the qualitative results are robust to the possibility of multihoming' by clients.

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