The catalytic activity of the histone deacetylase (HDAC) enzymes is directly relevant to the pathogenesis of cancer as well as several other diseases. HDAC inhibitors have been shown to have the potential to treat several types of cancers. The role of computational study of the HDAC enzymes is reviewed, with particular emphasis on the important role of molecular modeling to the development of HDAC inhibitors with improved efficacy and selectivity. The use of two computational approaches--one structure-based, and the second ligand-based--toward inhibitors against the different HDAC sub-classes, are summarized.