Ad Exchanges carry a pool of ad impressions. These are offered by the publishers in the hope that these will be bought. Buyers then buy the impressions they wish using technology such as DSP. The decisions are made in real-time based on information such as the previous behaviour of the user of an ad being served, time of day, type of device, ad position and many more.

The exchange is a digital market place. It brings together marketers and publishers. It facilitates buying and selling of advertising space; mostly through real-time auctions. They are used generally to sell display, video and mobile inventory.

The examples of exchanges are Right Media ( Yahoo ) and DoubleClick Ad Excange ( DoubleClick ).

Ad Exchanges are a mechanism which make the ad impressions from the publishers available to the DSPs. The price of each impression is decided through real-time auction called real-time bidding ( RTB ). A salesman is not needed to negotiate prices with buyers, since the impressions are auctioned off to the highest bidder.