Deposition is a term used in chemistry to describe the settling of particles or sediment from a solution or suspension mixture, or the production of a solid on a pre-existing surface.

The term is also widely used in earth science to describe the same process in a geological sense. Deposition of particles is an aggradational process — one that builds a landform — as opposed to a degradational process that erodes or reduces the size of a landform. For example, a river mouth delta is formed by deposition of sediment carried by the stream as the river current diminishes upon encountering the sea.

See also: deposition (meteorology), thin film deposition