RESEARCH Despite every cell in the human body having a nearly identical genetic sequence, divergent patterns of gene expression lead to the development of diverse cell types and functions. These patterns are established through epigenetic changes to the composition and structure of chromatin, the physiologic state of the genome. The repeating unit of chromatin is the nucleosome, in which segments of genomic DNA are wrapped around molecular spools of histone proteins. By displaying diverse combinations of histone post-translational modifications, the nucleosome serves as an active signaling hub in the regulation of genome-templated processes. These processes, including gene expression, DNA replication and DNA damage repair, play fundamental roles in cell development and maintenance of genomic integrity. As such, inappropriate regulation of the epigenetic enzymes that write, read and erase these modifications is correlated with many human diseases, especially cancer.