AdSense

AdSense is an ad serving application run by Google Inc. Website owners can enroll in this program to enable text, image, and video advertisements on their websites. These advertisements are administered by Google and 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 DoubleClick offering (also owned by Google). In Q1 2011, Google earned US$2.34 billion ($9.36 billion annualized), or 28% of total revenue, through AdSense.

History
Oingo, Inc., a privately held company located in Los Angeles, was started in 1998 by Gilad Elbaz and Adam Weissman. Oingo developed a proprietary search algorithm that was based on word meanings and built upon an underlying lexicon called WordNet, which was developed over the previous 15 years by researchers at Princeton University, led by George Miller.
Oingo changed its name to Applied Semantics in 2001, which was later acquired by Google in April 2003 for US$102 million.
In 2009, Google AdSense announced that it would now be offering new features, including the ability to "enable multiple networks to display ads".