This paper explores the extent to which nascent acquisitions can be investigated and challenged when necessary under existing merger control frameworks. It identifies the need to conduct an in-depth counterfactual analysis, to consider new investigative tools, and to ensure that any claimed efficiencies are tied to the specific transaction in question. It was prepared as a background note for a discussion held at the OECD in June 2020 on start-ups, killer acquisitions and merger control.