Abstract Pedogenic siderite is a carbonate mineral that forms in the reducing groundwaters of poorly drained soils and paleosols in zonal climatic belts with strongly positive precipitation–evaporation balances. Microcrystalline and spherulitic forms of siderite are commonly recognized in micromorphologic studies of hydromorphic paleosols. Ancient paleosol sphaerosiderites commonly occur with diameters in excess of 1 mm, while modern pedogenic siderite crystal dimensions in excess of 100 µm are rare. Pedogenic siderites have been widely reported from Late Paleozoic, Mesozoic, and Cenozoic paleosols. The carbon and oxygen isotopic compositions of pedogenic siderites have been widely used as proxies for the oxygen isotopic composition of paleoprecipitation for their respective paleosols. Modern process studies of historic pedogenic siderites are yielding a more refined understanding of the stable isotopic systematics of low-temperature siderite. These works will lead to a future change in usage of published siderite–water 18 O fractionation equations.