Cut through the complexity of today's niche ad networks with this at-a-glance review.

For a long time, ad networks were considered repositories of remnant, low-cost inventory; the "bottom of the barrel." However, in recent years the legitimization of the ad network model has been a boon to both advertisers and publishers. Almost every premium site allocates some of its inventory to the ad networks, and the networks offer advertisers relatively efficient, scalable inventory opportunities. Now that the model has been validated for web advertising, new networks are cropping up to address myriad niche opportunities: video, mobile, games, RSS feeds and podcasts.

Most of these companies operate similarly to DoubleClick in its very early days, as both a network and an enabling technology. However, while the market has become flooded with startups looking to establish an early beachhead in these categories, most of these technologies and platforms are still in their infancy. Many of them are plagued by infrastructure challenges and deployment complexities. There is also a lack of standardization that adds to the difficulty of executing buys. Additionally, CPMs vary widely and are relatively high for platforms that are still proving their efficacy.

Scale is another stumbling block, since there is a lack of available inventory in some categories. Many of these platforms suffer from a chicken and egg dilemma, as they try to grow advertiser demand and advertisers wait until the media matures. While advertiser demand is still low, it is growing, in some cases quite rapidly. Yet not every platform, device and opportunity is right for every advertiser.

To help you cut through the complexity, here are brief descriptions of the major characteristics of today's niche ad networks, each one accompanied by a list of ad networks that fit the descriptions.

Note: Many of the networks we list in the following pages offer a range of services and therefore appear in multiple appropriate categories.

Author notes: Marissa Gluck is founder and managing partner of Radar Research. Read full bio.