Google uses its Internet search technology to serve advertisements based on website content, the user's geographical location, and other factors. Those wanting to advertise with Google's targeted advertisement system may enroll through Google AdWords. AdSense has become a popular company in creating and placing banner advertisements on a website, because the advertisements are less intrusive than most banners, and the content of the advertisements is often relevant to the website.
Many websites use AdSense to monetize their content; it is the most popular advertising network. AdSense has been particularly important for delivering advertising revenue to small websites that do not have the resources for developing advertising sales programs and sales people to generate revenue with. To fill a website with advertisements that are relevant to the topics discussed, webmasters place a brief HTML code on the websites' pages. Websites that are content-rich have been very successful with this advertising program, as noted in a number of publisher case studies on the AdSense website. AdSense publishers may only place three ad units per page.
Some webmasters put significant effort into maximizing their own AdSense income. They do this in three ways:
- They use a wide range of traffic-generating techniques, including but not limited to online advertising.
- They build valuable content on their websites that attracts AdSense advertisements, which pay out the most when they are clicked.
- They use text content on their websites that encourages visitors to click on advertisements. Note that Google prohibits webmasters from using phrases like "Click on my AdSense ads" to increase click rates. The phrases accepted are "Sponsored Links" and "Advertisements".
 HistoryOingo, 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".
 AdSense for FeedsIn May 2005, Google announced a limited-participation beta version of AdSense for Feeds, a version of AdSense that runs on RSS and Atom feeds that have more than 100 active subscribers. According to the Official Google Blog, "advertisers have their ads placed in the most appropriate feed articles; publishers are paid for their original content; readers see relevant advertising—and in the long run, more quality feeds to choose from."
AdSense for Feeds works by inserting images into a feed. When the image is displayed by a RSS reader or Web browser, Google writes the advertising content into the image that it returns. The advertisement content is chosen based on the content of the feed surrounding the image. When the user clicks the image, he or she is redirected to the advertiser's website in the same way as regular AdSense advertisements.
AdSense for Feeds remained in its beta state until August 15, 2008, when it became available to all AdSense users.
 AdSense for searchA companion to the regular AdSense program, AdSense for search, allows website owners to place Google Custom Search boxes on their websites. When a user searches the Internet or the website with the search box, Google shares 51% of the advertising revenue it makes from those searches with the website owner. However the publisher is paid only if the advertisements on the page are clicked; AdSense does not pay publishers for regular searches. Web publishers have reported that they also pay a range from $0.64 to $0.88 per click.
 AdSense for domainsAdSense for domains allows advertisements to be placed on domain names that have not been developed. This offers domain name owners a way to monetize domain names that are otherwise dormant or not in use. AdSense for domains is currently being offered to all AdSense publishers, but it wasn't always available to all.
On December 12, 2008, TechCrunch reported that AdSense for Domains is available for all US publishers.
On February 22, 2012, Google announced that it was shutting down its Hosted AdSense for Domains program.
 AdSense for videoAdSense for video allows publishers with video content to generate revenue using ad placements from Google's extensive Advertising network including popular YouTube videos.
How AdSense works
- For contextual advertisements, Google's servers use a cache of the page to determine a set of high-value keywords. If keywords have been cached already, advertisements are served for those keywords based on the AdWords bidding system. (More details are described in the AdSense patent.)
- For site-targeted advertisements, the advertiser chooses the page(s) on which to display advertisements, and pays based on cost per mille (CPM), or the price advertisers choose to pay for every thousand advertisements displayed.
- For referrals, Google adds money to the advertiser's account when visitors either download the referred software or subscribe to the referred service. The referral program was retired in August 2008.
- Search advertisements are added to the list of results after the visitor performs a search.