Ian Ball continues MIT's course 14.12, Economic Applications of Game Theory, with a session on ad auctions. He opens by reviewing revenue equivalence, the result showing that different auction formats can yield the same expected revenue under certain conditions, then applies the framework to keyword search auctions of the kind Google runs to sell ad placement. The lecture works through how bidders value position and click-through rates, and how mechanism design choices affect the revenue a platform can extract. Delivered as a blackboard lecture at MIT, it assumes familiarity with the course's earlier auction theory material and builds directly on it, extending classroom game theory to a real market that runs billions of dollars in transactions daily.