We study the optimal (i.e. revenue maximizing) auction of multiple products
. We make three major points. First, we extend the relationship between pri
ce discrimination and optimal auctions from the single-product case to the
multiple-product case. A monopolist setting prices for multiple products ma
y offer discounts on purchases of bundles of products; similarly, the optim
al auction of multiple products facilitates price discrimination by allocat
ing products inefficiently to customers who are willing to purchase both pr
oducts. Second, we demonstrate that optimal auctions are qualitatively dist
inct from monopoly sales of multiple products. Because of uncertainty about
the values of other consumers, two products are bundled probabilistically
in an optimal auction for a customer who is willing to buy both of them. A
customer may then receive a discount on a lower-valued product without rece
iving a higher-valued product. Third, we show that in an optimal auction of
two products the allocation of one product may vary with the amount of com
petition for the other product.