Ad exchanges eliminate complexity and inefficiency by auctioning individual ad impressions in “real-time” between multiple advertisers, and selling them to the highest bidder; this auction process ensures that publishers maximize their revenue. Ad exchanges provide a single point of contact between publishers and ad buyers which improves efficiency. They also provide impression level data on visitors and web pages to advertisers, enabling them to modify their buying strategies based on real-time feedback. Exchanges also make it easy for both publishers and networks to fulfill campaigns, by delivering each impression when it is sold, instead of selling it in advance selling based on forecasts.