Google's context-sensitive advertising program is called Adsense ™. This program combines several of Google's strengths: their Adwords keyword-based advertising program and their ability to index web pages and uunderstand their content.
Adsense allows website owners to deliver Google ads on their pages and receive a share of the revenue when visitors click on the ad. The unique functionality of Adsense allows ads to be targeted at the page content, making the ads more relevant and presumably maximizing click-through and revenue for the site owner and Google. The ability to deliver ads related to the page content is what separates Google Adsense from conventional banners or other ad programs.
Web site publishers have found Adsense to be the easiest way to monetize sites, since no advertising sales effort is needed and the ads are automatically targeted to the page they appear on. Some web entrepreneurs have carried Adsense revenue generation to the next level by creating sites specifically to run Adsense ads. By optimizing the site to appear in natural search results, these entrepreneurs earn their income when visitors arrive at the site and click an Adsense ad.
Adsense and Click Fraud. Because site owners earn money when visitors click on their ads, the less scrupulous ones may be tempted to click on their ads to boost revenue. Google employs a variety of techniques to reduce click fraud, and site owners are often dropped from the program for clicking on their ads.