Recent progress in deciphering the genetics of Arabidopsis root development has been driven by the availability of novel molecular tools. For instance, combining enhancer trap lines and microarray analyses enabled the creation of an expression map for over 22000 genes at cellular resolution. Such expression profiles often suggest redundant action of homologous genes, which has indeed been observed for several pivotal factors that are required for the organization and maintenance of root meristems. Additional regulators of root development are also being identified by analysis of natural genetic variation. Moreover, microRNA control of gene expression has recently been implicated in root development, and progress has been made in understanding the interplay between environmental and genetic factors in root branching.