Before the current wave of consolidation, ad networks essentially positioned themselves in one of three ways:

1. Remnant repositories: Networks that bought or represented remnant inventory and resold it offered marketers cost-efficient reach and/or cost-efficient actions. They essentially strip-mined a massive supply of low-cost inventory to reach marketers' goal metrics as efficiently as possible. Companies such as ValueClick, Casale Media, Undertone Networks and many others operate in this space.
   
2. Behavioral targeting: Not unlike the above model, these networks typically bought or represented remnant inventory but added value through behavioral targeting. Marketers are able to reach the same anonymous user over many properties and target advertising to them based on their behavior across the network. Both Tacoda and Revenue Science are among the leaders offering behavioral targeting on their networks.
   
3. Content and context: Networks aggregated and sold inventory based on content, offering loose targeting parameters, such as sports and finance. This strategy was essentially the "poor man's" content play, allowing networks to offer similar reach to the major publishers such as Yahoo or Disney, if not always the same inventory. Within this category, a marketer can find networks such as Blue Lithium, offering branded, content-focused inventory as well as Google AdSense, focusing on unbranded, contextually relevant inventory.