In both the World Reference Base for Soil Resources (WRB) [1] and the USDA soil taxonomy, [2] a Histosol is a soil consisting primarily of organic materials. They are defined as having 40 centimetres (16 in) or more of organic soil material starting within 40 cm from the soil surface.

Histosols have a high content of organic matter and no permafrost. Most are saturated year round, but a few are freely drained. Histosols are commonly called bogs, moors, peats, or mucks. The central concept of Histosols is that of soils that are dominantly organic. They are mostly soils that are commonly called bogs, moors, or peats and mucks.

Histosols (from Greek histos, "tissue") are soils that are composed mainly of organic materials. They contain at least 20-30% organic matter by weight and are more than 40 cm thick. Bulk densities are quite low, often less than 0.3 g cm3.

Histosols are formed under waterlogged conditions typical of peat bogs, moors, and swamps. Under such conditions, the accumulated tissues of dead plants and animals and their decomposition products are preserved, resulting in soils of high organic content.

Histosols are soils that are composed mainly of organic materials. They contain at least 20-30% organic matter by weight and are more than 40 cm thick. Histosols typically form in settings where poor drainage inhibits the decomposition of plant and animal remains, allowing these organic materials to accumulate over time.

Histosols are unlike all other soils in that they are formed in 'organic soil material' with physical, chem-ical and mechanical properties that differ strongly from those of mineral soil materials. ‘Organic soil material’ is soil material that contains more than 20 percent organic matter by weight, roughly equiva-lent to 30 – 35 percent by volume.

Even though Histosols are composed of mainly organic materials (vegetation), they require a wet, saturated environment that limits decomposition. Cooler climates also limit decomposition, promoting accumulation of organic materials.

Histosols are soils that consist of dominantly organic soil materials. Histosols comprise only a small portion of the world's land area (1.2%), but are widely distributed irrespective of climate. They develop where the rates of organic matter accumulation exceed decomposition and removal.

Although pedologists have been evolving a classification for soils for many years, a comprehensive system for organic soils (Histosols) was largely neglected until the 1950's.

Generally, soils with a surface organic layer >40 cm thick have been classified as Histosols in the U.S. soil classification system—Soil Taxonomy (Soil Survey Staff 2014). Permafrost-affected organic soils are classified as the Histels sub-order in the Gelisols order (Soil Survey Staff 2014).