Over the last two decades, online advertising has become one of the most important elements of corporate communications. Whereas static banner ads dominated initially, search advertising (Varian 2007) now encompasses the largest part of global online advertising spending. In recent years, a new form of online advertising, real-time advertising (RTA), has been increasingly used. RTA is based on auctions in which individual advertising spaces are sold within a few milliseconds after calling a website. Advertisers or their media agencies participate in these auctions. In addition to Internet users, publishers and advertisers, additional technology service providers are involved in the RTA process. These service providers include supply-side platforms (SSP) that are commissioned by the publishers to offer advertising space in the market places. These market places are known as ad exchanges.