Google AdSense is a program that helps websites earn money by displaying targeted Google ads on their websites.
Google launched the AdSense program in June 2003 for English language websites and today, it has become the most popular advertising program among web publishers worldwide who are looking to monetize their online content.
According to Wikipedia, Google earned around US$2 billion, or 30% of total revenue, through AdSense along in the first quarter of 2010.