The history of mountain climbing evokes images of imperial domination, national rivalries, and competition between individuals. My project explores mountaineering from a transnational perspective and mountains as sites of cooperation. Tracing networks between alpine clubs across political fault lines, I explore how mountaineers negotiated the usage, risk, and environment of mountain spaces in the long twentieth century. Mountaineers formed an epistemic community which contributed to the conceptualization of mountains as an abstract spatial category through the standardization of levels of uncertainty and risk—such as degrees of climbing difficulties, objective risks, and avalanche danger. At the center of the story is the development of “alpine internationalism,” which expressed the belief that certain themes, issues, and problems relating to mountains require cross-border exchange or even a permanent international organization. The project furthermore introduces a new group of protagonists into the history of mountaineering. The central story is one of small states in East Central Europe. Mountaineers from Czechoslovakia, Poland, Hungary, and Yugoslavia emerge as active shapers of the transnational alpinist community rather than as victims of imperial forces, demographic circumstances, and nationalist imperatives. Internationalism offered a tool for the marginalized states to overcome the divisions of a formerly shared Habsburg space and at the same time assert their ranks in a larger European community. In the Cold War, encounters between Soviet and Western alpinists provided an unsurpassed opportunity for citizen diplomacy outside of the controlled environments in which standard forms of choreographed East-West exchanges took place.