Chromatin-modifying proteins mold the genome into areas that are accessible for transcriptional activity and areas that are transcriptionally silent. This epigenetic gene regulation allows for different transcriptional programs to be conducted in different cell types at different timepoints-despite the fact that all cells in the organism contain the same genetic information. A large amount of data gathered over the last decades has demonstrated that deregulation of chromatin-modifying proteins is etiologically involved in the development and progression of cancer. Here we discuss how epigenetic alterations influence cancer development and review known cancer-associated alterations in chromatin-modifying proteins.