 We're going to talk about auctions in this segment, and when we think about auctions, we usually think about something fairly specific, often something fairly simple. This is probably what many of us think of when we think about auctions initially. An art auction, where the auctioneer displays the art, and people from the audience call out larger and larger numbers until nobody says anything, and the auctioneer famously says going once, going twice, sold, and that's how the sale is decided on. Somewhat differently is this. What is this? Well, this is the flower market in Holland, just outside Amsterdam, and here every day large number of flowers are trucked in and sold, sold rather quickly because flowers are perishable, and they're sold somewhat differently. There is a trading pit where the pallets of flowers are rolled in, and they are auctioned off, auctioned off rather differently. You see these large clocks in the background, and they have a special role, and what that is, is something to be discussed. Here's a very different kind of auction. These are auctions for the rights to use our electric magnetic spectrum. So our airwaves are filled with all kinds of broadcasts from television to cellular to what have you, and those are worth a lot to commercially and socially. So governments all over the world have auctioned off the rights to use the spectrum, famously starting with the US FCC, or Federal Communication Commission. Besides being valuable to society and fetching very large sums into billions, these auctions are very interesting because they're complicated. What's being sold here is not something as simple as a single piece of art or even a pallet of flowers. What's sold here are regions and frequencies, and so different regions in the country are different goods, and in each region one can broadcast at different frequencies. So that makes for a different kind of auction where both the design of the auction and the trading in the auction are non-trivial. And finally, in all those cases until now, we've had a single seller and many buyers. Here's a famous example. We have many sellers and many buyers. This is the NASDAQ, one of the many stock exchanges in the world. We have many buyers and many sellers of goods, and in fact these goods come in multiple units. If you wish to buy Google stock, then you can buy many such shares, and there are many others like you want to buy it and many who want to sell it. So the way you design a two-sided exchange and the way you trade in it, and again different from the simple single-sided auction we know. These are all examples of auctions. There are many other examples and the theory about how the design and how to behave in auctions is very rich.