Reversible histone acetylation is one of the key mechanisms involved in the epigenetic control of gene expression. A variety of recent studies has revealed a role for acetylation in a much broader repertoire of physiological processes, including proliferation control and protein folding, and has highlighted how a variety of non-histone regulatory proteins are influenced by acetylation. Inhibition of histone deacetylase (HDAC) prompts tumour cells to enter apoptosis and, as a consequence, several HDAC inhibitors have entered clinical trials. It is likely that HDAC inhibitor drugs will provide an important class of new mechanism-based therapeutics for cancer.