What is a banner network?

A banner network is a group of websites that sell their advertising space in one centralized location. To the advertiser, it gives you the opportunity to purchase banner ad space over several sites, and track the results through one centralized source. With a diverse network of websites at your fingertips, you can fine tune your campaign to serve more ads to the productive sites and take impressions away from the unproductive ones. Some examples of banner ad networks are Tribal Fusion and Doubleclick.