Google launched interest-based advertising  back in 2009, which allowed advertisers to target consumers based on their Web behaviors—regardless of the content of the site they're currently on—and has been slowly introducing the capability to groups of advertisers over the past two years. Now, Google has announced  that it’s making interest-based ads available to all of its AdWords advertisers.
On its official blog, Google explained that its AdWords system looks at the types of pages a user visits, including how recently and frequently they’ve visited, and then associates the user’s browser with relevant interest categories. Advertisers can then use those categories to target specific customers, even if the customer is on a completely unrelated site. Users are also able to change the categories they’re associated with, or opt out of the advertising cookies entirely.
Advertisers can choose from over 1,000 interest categories and will pay for clicks or impressions at auction prices. So far, the interest-based advertising has been successful. “Our beta advertisers have used interest categories to successfully meet all kinds of goals, from an advertiser increasing brand lift by 40 percent to a shoe retailer driving 400 percent more conversions at a lower advertising cost per sale,” said Google.