Users of search engines (SEs) are often regarded as the primary constituents of successful SEs. The paying customers, namely advertisers, enable the free services that SEs provide and yet they are not as well understood as the user population. We discuss several studies that focus on advertisers: methods for evaluating usefulness of new tools to manage their campaigns, and methods for assessing campaign effectiveness. We also introduce the concept of advertiser graphs as a vehicle to better understand advertisers and their inter-relationships.