The document summarizes the history and evolution of media buying over the past 300+ years, focusing on the past 10 years of media exchange buying and real-time bidding (RTB). It outlines the transition from direct publisher sales in newspapers/magazines (1700s) to television spots/upfronts (1950s) to digital media buying (1990s). It then details the development of media exchanges (2000s) and the rise of RTB bidding through exchanges from 2008 onward. Finally, it discusses the current state of exchanges, buying metrics needed for RTB, and the future potential of infinite inventory and real-time consumer experiences through exchanges.