Climbing guidebook in the context of Base camp

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.

Unlike most sports, mountaineering lacks widely applied formal rules, regulations, and governance; mountaineers adhere to a large variety of techniques and philosophies (including grading and guidebooks) 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 the 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.

In mountaineering and climbing, a first ascent (abbreviated to FA in guide books), is the first successful documented climb to the top of a mountain peak or the top of a particular climbing route. Early 20th-century mountaineers and climbers were mainly focused on reaching the tops of notable mountain peaks (e.g. the eight-thousanders such as Mount Everest) and the tops of iconic climbing routes (e.g. the great north faces of the Alps such as the Eiger) by whatever means possible, and often using considerable amounts of aid climbing and/or with large expedition style support teams allowing them to "lay siege" to the climb.

As all the key tops were summited, the manner or "style" in which each top was reached became important to climbers, and particularly the ability to complete the ascent without the use of any artificial aids, which is called free climbing. In free-climbing, the term first free ascent (abbreviated FFA) denotes where a mountain or climbing route is ascended without any artificial aid — note that equipment for protection in the event of a fall can be used as long as they did not aid in the climber's upward progression. Completing the FFA of a climbing route is often called freeing (or more latterly sending) a route, and is highly coveted.

Rock climbing is a climbing sports discipline that involves ascending routes consisting of natural rock in an outdoor environment, or on artificial resin climbing walls in a mostly indoor environment. Routes are documented in guidebooks, and on online databases, detailing how to climb the route (called the beta), and who made the first ascent (or FA) and the coveted first free ascent (or FFA). Climbers will try to ascend a route onsight, however, a climber can spend years projecting a route before they make a redpoint ascent.

Routes range from a few metres to over a 1,000 metres (3,300 ft) in height, and traverses can reach 4,500 metres (14,800 ft) in length. They include slabs, faces, cracks and overhangs/roofs. Popular rock types are granite (e.g. El Capitan), limestone (e.g. Verdon Gorge), and sandstone (e.g. Saxon Switzerland) but 43 types of climbable rock types have been identified. Artificial indoor climbing walls are popular and competition climbing — which takes place on artificial walls — became an Olympic sport in 2020.

A climbing route (German: Kletterrouten) is a path by which a climber reaches the top of a mountain, a rock-face, or an ice-covered obstacle. Climbing routes are recorded in a climbing guidebooks and/or in online climbing-route databases. Details recorded include the type of climbing route (e.g. bouldering route, sport climbing route, traditional climbing route, ice climbing route, or alpine climbing route, etc.), the difficulty grade of the route–and the beta for its crux(es)–including any risk or commitment-grade, the length and number of pitches of the route, and the climbing equipment (e.g. climbing protection gear) that is needed to complete the route.

Definitions have been agreed on what determines a valid ascent of a route (e.g. the redpoint in rock climbing), and on the classes or styles of ascent (e.g. onsighted, flashed). The coveted first ascent (FA), first free ascent (FFA), and first female free ascent (FFFA), are chronicled for most routes. After a route is established, variations can be created (e.g. directessimas, sit starts, or enchainments), and climbers will try to improve on the style in which the route is climbed (e.g. minimizing aid climbing or removing other supports such as oxygen or fixed ropes). Some climbers will try to reduce or limit the in-situ climbing protection (e.g. greenpointing) or will try to completely free-solo the route. Others seek to set speed climbing records on routes.

Beta is a climbing term that designates information about how to ascend a climbing route, and the specific climbing techniques required—and how to apply them—to overcome the key challenges encountered. Traditionally sourced in climbing guidebooks, online databases and apps now provide detailed climbing beta. The term is attributed to Texan climber Jack Mileski.

When a climber completes a route on their first attempt and without falling, it is called an onsight if they had no beta, or a flash if they had beta (a completion after several failed attempts is called a redpoint). New grade milestones in the on-sighting and flashing of routes are actively followed in the climbing media. The discovery of new beta has led to the re-grading of notable and historic climbing routes.