The neocortex, a structure that is unique to mammals, is formed by balanced proliferative and differentiative divisions of neural stem and progenitor cells that give rise to differentiated neural cells–neurons and glia. During neurogenesis, coordinated gene expression programs drive neural progenitor cells to initially expand their pool and to subsequently generate different neuronal subtypes, before switching to gliogenesis. Epigenetic mechanisms are important in the regulation of cell fate specification during development. In this chapter, we will focus on one type of epigenetic modification–histone methylation–that regulates neural progenitor behaviour and neuronal function. Importantly, mutations in several histone modifying enzymes have been reported in patients with neurodevelopmental disorders, often linked to intellectual disability. We will review the molecular and cellular functions of these enzymes and discuss their contribution to the human phenotypes.