A makhtesh (Hebrew: מַכְתֵּשׁ‎‎ ([maχˈteʃ]), plural: מַכְתְּשִׁים ([ˈmaχtəˌʃim]) – Makhteshim) is a geological landform considered unique to the Negev desert of Israel. A makhtesh has steep walls of resistant rock surrounding a deep closed valley which is usually drained by a single wadi. The valleys have limited vegetation and soil, containing a variety of different colored rocks and diverse fauna and flora. The best known and largest makhtesh is Makhtesh Ramon.

Although commonly referred to as "craters," these formations are "erosion cirques" (steephead valleys or box canyons). Craters are formed by the impact of a meteor or volcanic eruption, whereas makhteshim are created by erosion.

The word makhtesh is the Hebrew word for a mortar grinder (מַכְתֵּשׁ‎) . The geological landform was given this name, because of its similarity to the grinding bowl.

A hard outer layer of rock covered softer rocks. Erosion relatively quickly removes the softer minerals, and they are washed away from under the harder rock. The harder rocks eventually collapse under their own weight and a crater-like valley structure is formed. In Negev and Sinai makhteshim, the hard rocks are limestone and dolomites, while the inner softer rocks are chalk or sandstone.