The CCD defines desertification as land degradation in the drylands (" 'Desertification' means land degradation in arid, semi-arid and dry sub-humid areas."), yet the two terms are often used as if they are distinct (e.g., "Land degradation and desertification in desert margins" by Reich et al. 2000). The CCD also defines "land" by its primary productivity service (" 'land' means the terrestrial bioproductive system.") and "land degradation" as an implicit loss of provision of this service (" 'land degradation' means reduction or loss . of the biological or economic productivity .').

The definition of biological productivity and economic benefit depends on users' priorities - transforming woodland to cropland may decrease biological productivity, degrade the economic benefit of firewood production but increase the economic benefit of food production. With respect to the mechanisms of land degradation - changes in the properties of the land (soil, water, vegetation) do not correspond linearly to changes in productivity. Loss of productivity can also be attributed to non human-induced factors such as rainfall variability and human factors such as low labor input. Thus, a range of interacting variables that affect productivity should be addressed in order to assess objectively and unambiguously land degradation.

Commonly considered degradation processes are vegetation degradation, water and wind erosion, salinization, soil compaction and crusting, and soil nutrient depletion. Pollution, acidification, alkalization, and water logging are often important locally (Oldeman, 1994; Lal, 2001; Dregne, 2002). Field experiments, field measurements, field observations, remote sensing, and computer modeling are carried out to study these processes. The higher the aggregation level in each of these study approaches, the more problematic each of the methods becomes, either because of upscaling issues or because of questionable extrapolations and generalizations.