The numerous processes implicated in the rapid and profound climate-driven changes that are underway across the world's mountains must be well monitored, understood, and—as far as possible—accurately projected. However, not only are the available environmental data upon which such activities hinge often severely limited, but interdisciplinary consensus regarding which variables should be considered observation priorities also remains elusive. Here, the concept of Essential Mountain Climate Variables (EMCVs) is introduced as a potential means of ameliorating the situation. After a review of climate-driven environmental change in mountains, a preliminary set of corresponding EMCVs is proposed. Variables pertaining to several disciplines naturally feature prominently. In addition, several are not currently considered to hold broader global relevance, which justifies our mountain-specific approach. Established and emerging possibilities to measure, generate, and apply EMCVs are then summarized. Finally, future activities toward the concept's formalization are recommended. Ultimately, the approach hopes to increase the utility of mountainous environmental data to both fundamental science and decision making related to environmental management, risk mitigation, and adaptation.