This paper presents a broad retrospective evaluation of mergers and merger decisions in markets dominated by multisided digital platforms. First, we document almost 300 acquisitions carried out by three major tech companies—Amazon, Facebook, and Google—between 2008 and 2018. We cluster target companies on their area of economic activity providing suggestive evidence on the strategies behind these mergers. Second, we discuss the features of digital markets that create new challenges for competition policy.

By using relevant case studies as illustrative examples, we discuss theories of harm that have been used or, alternatively, could have been formulated by authorities in these cases. Finally, we retrospectively examine two important merger cases, Facebook/Instagram and Google/Waze, providing a systematic assessment of the theories of harm considered by the UK competition authorities as well as evidence on the evolution of the market after the transactions were approved. We discuss whether the competition authority performed complete and careful analyses to foresee the competitive consequences of the investigated mergers and whether a more effective merger control regime can be achieved within the current legal framework.