Introduction

AdSense is an ad serving application run by Google Inc. Website owners can enroll in this program to enable text, image, and more recently, 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).

During the summer of 2003, Google introduced a new ad delivery mechanism for website publishers (both large and small) known as Google AdSense. Earlier Google AdWords ads were only available for publishers with more than 20 million impressions per month. AdSense can now cater to small niche website publishers by bringing in content targeted advertisements to their websites.

From Google's own words :

"Google AdSense is a fast and easy way for website publishers of all sizes to display relevant, unobtrusive Google ads on their website's content pages and earn money. Because the ads are related to what your users are looking for on your site, you'll finally have a way to both monetize and enhance your content pages.

It's also a way for web site publishers to provide Google search to their site users, and to earn money by displaying Google ads on the search results pages."

Currently Google adsense is the best paying & most reliable source of income for webmasters. Adsense program consists display of google ads through adsense for web pages and through adsense for web search.