Companies such as Google and Facebook are not merely conglomerates of Internet-based services which just so happen to process personal data. They should instead be conceptualized as ‘data ecosystems’ and treated as such. Data ecosystems are companies which collect and monetize personal data through a network of widely diverging internet-based services, for the overarching purpose of targeted advertising. Contrasted with traditional conglomerates, a data ecosystem is unique since all of its different branches are interconnected through a single shared resource: personal data. Consequently, this ecosystem structure grants strong sources of market power. Network effects of personal data, throughout the entire ecosystem, lead to services being constantly updated and personalized with increasing accuracy, while simultaneously enhancing the monetization strategy of targeted advertising. Meanwhile, data ecosystems’ reach across the Internet means that consumers cannot realistically choose not to participate, nor find suitable competitors for each service. Finally, data ecosystems have strong incentives to expand into additional markets: conglomerate mergers are an essential strategy to reinforce their sources of market power. Data ecosystems enjoy a unique form of market power which has been seriously underestimated in the past. A new approach that fully appreciates their unique structure and market power is therefore required.