The Reference Soil Group of the Calcisols accommodates soils in which there is substantial secondary accumulation of lime. Calcisols are common in calcareous parent materials and widespread in arid and semi-arid environments. Formerly Calcisols were internationally known as `Desert soils' and `Takyrs'.

It is difficult to quantify the worldwide extent of Calcisols with any measure of accuracy. Many Calcisols occur together with Solonchaks that are actually salt-affected Calcisols and/or with other soils with secondary accumulation of lime that do not key out as Calcisols. The total Calcisol area may well amount to some 1 billion hectares, nearly all of it in the arid and semi-arid (sub)tropics of both hemispheres.

Many Calcisols are old soils if counted in years but their development was slowed down by recurrent periods of drought in which such important soil forming processes as chemical weathering, accumulation of organic matter and translocation of clay came to a virtual standstill. As a result, only an ochric surface horizon could develop and the modification of subsoil layers did not advance beyond the formation of a cambic subsurface horizon.

Many Calcisols are `polygenetic': their formation took different courses during different geologic eras with different climates. The argic subsurface horizon of many Calcisols is widely considered to be a relic from eras with a more humid climate than at present.