What is an ad exchange?
To understand ad exchanges, let’s first start with ad networks. Ad networks are companies that represent multiple websites and sell ads from across those websites. Ad networks initially fulfilled two main needs. first was to simplify buying across multiple websites. The second was to help smaller publishers, those who were not large enough to have their own representation, sell ads. By combining a group of small publishers, there was enough reach to attract advertisers.
it was an evolution of this second need that spawned ad exchanges. Ad exchanges, at least from the advertiser side, are similar to buying from an ad network. These ad exchanges were originally designed to aggregate and sell remnant ad inventory and inventory from small publishers. With a growth in popularity, an increasing amount of more premium inventory has become available on many ad exchanges. Because of the fragmentation of the inventory being sold on ad exchanges, they rely on technology platforms to manage their inventory. Right Media (yahoo!), DoubleClick (Google), openX, and Appnexus are a few of the major ad exchanges.