The DNA molecules in each one of the cells in a person’s body, if laid end to end, would measure approximately two metres in length. Remarkably, however, cells are able to fold and compact their genetic material in the confined space of the nucleus, which spans only a few micrometres. Importantly, the compaction and arrangement of the genome inside the nucleus needs to be achieved in an ordered fashion that still allows cells to access the genetic information appropriately, for example to produce messenger RNAs for specific proteins, or to replicate the genetic material prior to cell division. When mutations occur that disrupt features associated with the spatial organisation of the genome, this leads to developmental disorders and cancer.