99% of Google's revenue is derived from its advertising programs. For the 2006 fiscal year, the company reported $10.492 billion in total advertising revenues and only $112 million in licensing and other revenues.Google is able to precisely track users' interests across affiliated sites using DoubleClick technology and Google Analytics. Google's advertisements carry a lower price tag when their human ad-rating team working around the world believes the ads improve the company's user experience.Google AdWords allows Web advertisers to display advertisements in Google's search results and the Google Content Network, through either a cost-per-click or cost-per-view scheme. Google AdSense website owners can also display adverts on their own site, and earn money every time ads are clicked.Google began in March 2009 to use behavioral targeting based on users' interests.

Google has also been criticized by advertisers regarding its inability to combat click fraud, when a person or automated script is used to generate a charge on an advertisement without really having an interest in the product. Industry reports in 2006 claim that approximately 14 to 20 percent of clicks were in fact fraudulent or invalid.

In June 2008, Google reached an advertising agreement with Yahoo!, which would have allowed Yahoo! to feature Google advertisements on their web pages. The alliance between the two companies was never completely realized due to antitrust concerns by the U.S. Department of Justice. As a result, Google pulled out of the deal in November, 2008.