"Ever wonder what determines the order in which ads appear on your site? Then you've wondered about the Google AdWords ad ranking system. AdWords is the advertising platform thousands of advertisers use to place their ads on the Google network. Once an ad is in the AdWords system, it competes against other ads to appear on relevant pages in the AdSense network. It's through this real-time dynamic auction system that ads are ranked. Those ads with the highest Ad Rank at any given moment are displayed on your site."