Orogeny refers to forces and events leading to a severe structural deformation of the Earth's lithosphere (crust and uppermost mantle) due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts. The word "orogeny" comes from the Greek (oros for "mountain" plus genesis for "creation" or "origin"), and it is the primary mechanism by which mountains are built on continents. Orogens develop while a continental plate is crumpled and thickened to form mountain ranges, and involve a great range of geological processes collectively called orogenesis.

Formation of an orogen is accomplished in part by the tectonic processes of subduction, where a continent rides forcefully over an oceanic plate (noncollisional orogens), or convergence of two or more continents (collisional orogens).

Orogeny usually produces long arcuate (from arcuare, to bend like a bow) structures, known as orogenic belts. Generally, orogenic belts consist of long parallel strips of rock exhibiting similar characteristics along the length of the belt. Orogenic belts are associated with subduction zones, which consume crust, produce volcanoes, and build island arcs. The arcuate structure is attributed to the rigidity of the descending plate, and island arc cusps are related to tears in the descending lithosphere. These island arcs may be added to a continent during an orogenic event.