Chromatin is a nucleoprotein complex, found in eukaryotic organisms, consisting of approximately 50% DNA and 50% histone proteins. The histones undergo a number of reversible covalent chemical modifications (for example, acetylation, methylation, phosphorylation), especially in the N-terminal regions. These chemical changes prepare chromatin for a range of essential cellular processes and understanding the code for the many possible combinations of modifications, in terms of their function, is currently an area of intense research and is driving developments in molecular cancer therapies. Several molecules that modulate chromatin modifications have already been developed as commercially available cancer treatments, while many others are undergoing clinical trials.