Mergers and acquisitions rarely deliver on expectations, yet organizations continue to pursue these strategic decisions. Scholars have researched acquisitions extensively as decisions under risk (Kumar, Dixit, & Francis, 2015) but decision theorists define decisions under risk as decisions where alternatives come with known outcomes and probabilities. In real-world decisions, such as mergers and acquisitions, our knowledge of possible outcomes and their probabilities is rarely complete. Examining acquisitions as decisions under risk may have led researchers to incorrect conclusions or given an incomplete view of these critical strategic choices. In this research, I suggest that mergers and acquisitions are decisions made under ambiguity, or situations where outcomes and probabilities are only partially known (Knight, 1921; Raiffa, 1957; Takemura, 2014). Examining acquisitions as decisions under ambiguity may allow for further understanding of this phenomenon, as well as, how and why so many acquisitions fail. In this study, I conducted an initial qualitative study to identify and confirm sources of ambiguity. Using the information gained from study 1, I examined 140 acquisitions using archival data to study the relationship between ambiguity and acquisition performance. I also examined the role of the size of the acquisition and the decision-maker’s experience with acquisitions in this relationship.