The ad exchange puts the offer out for bid to demand-side platforms. Demand side platforms act on behalf of ad agencies, who sell ads which advertise brands. Demand side platforms thus have ads ready to display, and are searching for users to view them. Bidders get the information about the user ready to view the ad, and decide, based on that information, how much to offer to buy the ad space. According to the Internet Advertising Bureau, a demand side platform has 10 milliseconds to respond to an offer. The ad exchange picks the winning bid and informs both parties.
As advertisers collect data across multiple external websites about a user's online activity, they can create a detailed profile of the user's interests to deliver even more targeted advertising. This aggregation of data is called behavioral targeting. Advertisers can also target their audience by using contextual to deliver display ads related to the content of the web page where the ads appear.:118 Retargeting, behavioral targeting, and contextual advertising all are designed to increase an advertiser's return on investment, or ROI, over untargeted ads.
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