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What gives quantum computers that extra oomph over their classical digital counterparts? An intrinsic, measurable aspect of quantum mechanics called contextuality, it now emerges. See Article p.351 It is widely appreciated that quantum computing promises advantages over classical computing in certain circumstances and for certain problems. But what are the specific features of quantum mechanics that are ultimately responsible for this enhanced potential? Mark Howard and colleagues identify 'quantum contextuality' — a generalization of the concept of quantum non-locality — as the critical resource that gives quantum computers their power. This finding not only provides clarification of the theoretical basis of quantum computing, it also provides a framework for directing experimental efforts to most effectively harness the weirdness of quantum mechanics for computational tasks.