"Unknown unknowns," that is, future contingencies that lack an ex ante description for some decision-makers for whom the contingency is relevant, are fundamental to strategy theory and practice. And yet, most strategy research is founded on the assumption that the future can be described in terms of "known unknowns," that is, future contingencies that are known in principle (but whether and how they actually occur is unknown). We discuss the importance of unknown unknowns for strategy, focusing specifically on firm-level adaptation. We also discuss why prior literature has failed to address unknown unknowns, and outline key points that should be addressed by a program of research into the nature and role of unknown unknowns in strategy.