The document discusses the past, present, and future of ad servers. It notes that historically there was little competition in the ad server market, leading to stagnation, but that header bidding and other innovations have increased competition and driven more revenue for publishers. It provides examples of how header bidding increased revenue from one supply side platform (SSP) from 9% to 17% of revenue. It also discusses how AppNexus is innovating with techniques like open dynamic allocation, accurate forecasting, and viewable guarantees to continue increasing value for publishers.