An ad server is an online tool whose purpose is to make all aspects of ad management easier. Basically, this tool tackles all the advertising problems. That is why these tools are often used not only by advertisers, but also by networks and publishers. Ad servers can be used for a number of different purposes, including the monitoring of ad impressions and clicks gained by a campaign. Some publishers use them for keeping a track of free ad space on a certain website. Ad servers can also be used for targeting ads (including both geo and behavioral targeting), frequency capping, action tracking, and so on.