Monocot cereals develop a complex root system comprising embryonic roots at an early seedling stage and postembryonic roots which make up the fibrous root system of adult crops. In the model cereals maize, rice, and barley a number of mutants affecting root development have been identified in the past and a subset of the affected genes have been recently cloned and functionally characterized. The present review summarizes genetic and molecular data of cereal root mutants impaired in the elongation or initiation of embryonic and postembryonic roots and the elongation of root hairs for which the affected genes have been recently cloned.