Post-translational modifications of histone tails have dramatic ramifications on a variety of vital cellular functions. Removal of the acetyl groups from lysine residues is catalyzed by histone deacetylases (HDs). Many HDs are known to be components of multiprotein complexes such as SIN3 and NuRD that are involved in chromatin condensation and gene regulation. Plants contain a highly elaborated set of HDs with four distinct classes of these enzymes. Plant HDs have been implicated to play roles in transgene silencing, rDNA regulation, gene expression, and many developmental processes. Seventeen Arabidopsis HDs are apparent in Genbank as are numerous putative HD-interacting partners. Maize HDs have been extensively characterized biochemically and the use of powerful genetic tools currently available in Arabidopsis is rapidly accelerating the base of knowledge on the control circuitry of plant chromatin.