Histone deacetylases (HDACs), known for their ability to target histones as well as more than 50 non-histone proteins, are classified into three major classes according to their homology to yeast proteins, including class I (HDAC1, HDAC2, HDAC3 and HDAC8), class II (HDAC4, HDAC5, HDAC7 and HDAC9) and class IV (HDAC11). HDAC inhibitors, a large group of compounds that is able to induce the accumulation of acetylated histones as well as non-histone proteins, are divided into several structural classes including hydroxamates, cyclic peptides, aliphatic acids and benzamides. HDAC inhibitors have been investigated for their efficacy as anticancer agents in the treatment of a wild range of cancers.