A massif (/mæˈsiːf, ˈmæsɪf/) is a principal mountain mass,^[1] such as a compact portion of a mountain range, containing one or more summits (e.g. France's Massif Central). In mountaineering literature, a massif is frequently used to denote the main mass of an individual mountain.

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As a purely scientific term in geology, however, a "massif" is separately and more specifically defined as a section of a planet's crust that is demarcated by faults or flexures. In the movement of the crust, a massif tends to retain its internal structure while being displaced as a whole. A massif is a smaller structural unit than a tectonic plate and is considered the fourth-largest driving force in geomorphology.^[2]

The word "massif" originates from French (in which the word also means "massive"), where it is used to refer to a large mountain mass or compact group of connected mountains forming an independent portion of a range. The Face on Mars is an example of an extraterrestrial massif.^[3] Massifs may also form underwater, as with the Atlantis Massif.^[4]