This paper surveys competition problems in the search ads segment of the online advertising industry. We review the economics of the activity, remarking the incentives a dominant provider has under the network effects that characterize the industry. We discuss the most prominent literature...

We develop a model with many advertisers (products) and many advertising markets (media). Each advertiser sells to a different segment of consumers, and each medium has a different ability to target advertising messages. We characterize the competitive equilibrium in the media markets and...