The networks themselves are ad agencies and companies that partner with advertisers and publishers to buy and sell ads on sites they dont own.

AdSense publishers will now be able to allow advertisers from these networks to compete directly with AdWords advertisers for their ad space. The ad networks Connect advertisers with publishers Provide access to additional inventory not currently available with AdWords Adhere to Googles standards for user privacy, ad quality and speedReporting and payments will still run through AdSense as always, and available ad formats will remain the same as they have been for AdWords. Publishers will still have control over which networks can show ads on their pages, and they can choose to opt out of receiving ads from specific networks, or all networks.Right now, the feature is only available to publishers in North America and Europe, but Google plans to rolling out to more places in the future.