"The advertising system, announced at the Official Google Blog on Wednesday, increases Google’s level of advertising customization. The company’s AdSense network (which generates the ads within Google Search, Gmail, and other Google properties) had already been selecting ads based on your current activity: If you searched for "video card," for example, the ads on the right would be related to computer components. Now, however, the system will delve deeper, using data from the past in addition to the present.
"Advertisers need an efficient way to reach those who are most interested in their products and services," says Susan Wojcicki, Google’s VP of product management. "Publishers can generate more revenue when they connect advertisers to interested audiences."" – Content courtesy of Google’s Behavioral Ad Targeting: How to Reclaim Control – PC World