AdSense

Google AdSense is a program run by Google Inc which enables publishers in the Google Network of content sites to automatically serve text, image, video, and rich media ads that are targeted to site content and audience. These advertisements are administered, sorted, and maintained by Google, and they can generate revenue on either a per-click or per-impression basis. Google beta tested  a cost-per-action service, but discontinued it in October 2008 in favor of a Double Clickoffering (also owned by Google). In Q1 2011, Google earned US$2.34 billion ($9.36 billion annualized), or 28% of total revenue, through AdSense