Coprecipitation is one of the classical, but quite useful, techniques for separation/preconcentration for trace element analysis. Many elements can be easily collected with a carrier precipitate, and the handling is simpler and easier compared to that of other techniques such as solvent extraction and solid-phase extraction. In addition, selective separation can also be designed by controlling of chemical and physical conditions in the procedure. In this section, mechanisms of coprecipitation, selection of a carrier precipitates, selectivity in coprecipitation, and typical examples of coprecipitation in trace element analysis are described.