Mountaineering, mountain climbing, or alpinism, is a set of outdoor activities that involves ascending mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas that have become sports in their own right. Indoor climbing, sport climbing, and bouldering are also considered variants of mountaineering by some, but are part of a wide group of mountain sports.

Mountaineering activity, involving such activities as mountain climbing and trekking, has traditionally been dominated by men. Although women's participation in mountaineering has grown, the gender gap is still pronounced in terms of quantitative engagement in these forms of sport tourism. Yet, in competitive mountaineering, the success rate of females is currently higher than that of males

Unlike most sports, mountaineering lacks widely applied formal rules, regulations, and governance; mountaineers adhere to a large variety of techniques and philosophies when climbing mountains. Numerous local alpine clubs support mountaineers by hosting resources and social activities. A federation of alpine clubs, the International Climbing and Mountaineering Federation (UIAA), is the International Olympic Committee-recognized world organization for mountaineering and climbing. The consequences of mountaineering on the natural environment can be seen in terms of individual components of the environment (land relief, soil, vegetation, fauna, and landscape) and location/zone of mountaineering activity (hiking, trekking, or climbing zone). Mountaineering impacts communities on economic, political, social and cultural levels, often leading to changes in people's worldviews influenced by globalization, specifically foreign cultures and lifestyles.