Peak bagging or hill bagging is an activity in which hikers, climbers, and mountaineers attempt to reach a collection of summits, published in the form of a list. This activity has been popularized around the world, with lists such as 100 Peaks of Taiwan, four-thousand footers, 100 Famous Japanese Mountains, the Sacred Mountains of China, the Seven Summits, the Fourteeners of Colorado, and the eight-thousanders becoming the subject of mass public interest.

There are numerous lists that a peakbagger may choose to follow. A list usually contains a set of peaks confined to a geographical area, with the peaks having some sort of subjective popularity or objective significance, such as being among the highest or most prominent of the area. Some maps and lists may be inaccurate, however, which has implications for climbers and peak-baggers who rely on publicly reported data.

Although peak bagging is a fundamental part of the sport of mountaineering, the term is strongly associated with hiking and other non-technical activities like snowshoeing. A handful of lists, such as the eight-thousanders and the Alpine four-thousanders, have an extremely high reputation among mountaineers, but in general the term "peak bagging" is a pejorative to many climbers.

Peak bagging is distinguished from highpointing, where the goal is to reach the highest point in some geographic area (e.g. county, state, or country), whether or not it is a peak.