A makhtesh is a geological landform regarded to be unique to the Negev desert of Israel and the Sinai Peninsula. Although commonly regarded to be "craters", these structures are more accurately described as erosion cirques. 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 a diverse fauna and flora which has been protected and preserved over millions of years. The best known makhtesh is Makhtesh Ramon of Israel's Negev desert.

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. ] In most cases, makhteshim only have one drainage system, although the Makhtesh Ramon has three.

The Hebrew term makhtesh is usually translated as "crater" although there is a difference between the two: Makhteshim are formed by water erosion whereas craters are formed by the impact of a meteor or volcanic eruption. A more accurate translation is therefore "erosion cirque."

Makhtesh Ramon is exceptional as it is drained by two rivers (Nahal Ramon and Nahal Ardon). It is the largest Makhtesh at over 40km long, 2-10km wide and over 500m deep. The rocks in this makhtesh contain thousands of ammonite fossils, as well as peats from ancient volcanos.
Makhtesh Gadol (Large Makhtesh) At the time of naming, the Makhtesh Ramon was unchartered and so this was thought to be the largest Makhtesh.