The Google DoubleClick: Ad Exchange
Ad Exchanges are a progression of two major influences in digital media trading: performance-based buying approaches combined with selling the huge volume (often remnant) of display inventory in ad networks. Ad exchanges are not a new phenomenon. MSN, Yahoo and others already offer networked display advertising inventory sold against performance based pricing models, primarily based on a cost per click (CPC), cost per thousand (CPM) or cost per acquisition/ sale/ lead (CPA/S/L) basis. In contrast, Google's Ad Exchange is an open auction in which a bid for inventory is made in real time. However, the model will be different than search bidding where success in the auction determines ranking on a page from position one, winning through position two, three, etc. The Google Ad Exchange bidding model has only two outcomes; you either win the impression or you don't. There are no second positions on the page.
Google believe their Ad Exchange has three key benefits: