Nickel (Ni) may be an environmental pollutant. It is phytotoxic as well as zootoxic, especially to marine life. It results in carcinogenesis and many other metabolic complications. The main sources of environmental contamination of Ni are nickel refineries, industrial and municipal wastes, and auto emissions. No matter what the sources of environmental contamination, soils and sediments are the ultimate receptacles of Ni. Nickel is introduced into human and animal food chains mainly through water and plants. One way of understanding the chemical behavior of Ni in soils is by simulating thermodynamic stability models of various Ni minerals and solution species in soils. The objectives of this paper are to develop such stability models of probable Ni minerals and solution species in soils and to discuss their role in a soil environment.