In geology, a massif ( or ) is 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. The term also refers to a group of mountains formed by such a structure.

In mountaineering and climbing literature, a massif is frequently used to denote the main mass of an individual mountain. The massif is a smaller structural unit of the crust than a tectonic plate, and is considered the fourth-largest driving force in geomorphology.

The word is taken 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. One of the most notable European examples of a massif is the Massif Central of the Auvergne region of France.

The Face on Mars is an example of an extraterrestrial massif.

Massifs may also form underwater, as with the Atlantis Massif.