Ad networks are advertisement agencies and companies, who are certified by Google so as to ensure that they adhere to (and can be included to) Adsense standards for user-privacy, Ad quality, and speed. They make it possible for advertisers and interested publishers to buy and sell adverts on various Web sites thus increasing the competition for ad spaces on Web sites and consequently potentially higher earnings in the long run. Although enabled by default, publishers can also use category filters to control the type of adverts that are displayed on their Web sites in the Ad Review Centre.
However, Google does not guarantee immediate increase in Ad earnings with Google Ad-networks, rather it hopes that as the amount of Ad networks increases, the scheme will eventually become more profitable for Web publishers.
Talking Point
Have you noticed any difference in Ad earnings since you started using Google-certified Ad networks to compliment Adsense?
