During early embryonic development and gametogenesis, DNA methylation is established by the de novo DNA methyltransferases DNMT3A and DNMT3B, together with cofactors such as DNMT3L. After every cell cycle, DNMT1 maintains methylation patterns in daughter cells. DNMT1 recognizes replication foci and hemi-methylated DNA with the help of PCNA and UHRF1, respectively. HELLS, CDCA7 and ZBTB24 (gray) contribute to DNA methylation maintenance at intergenic regions and repetitive elements. DNA methylation can be passively removed, for example, through the absence or inhibition of DNMT1. Active demethylation occurs through the oxidizing activity of TET enzymes. Abbreviations: CDCA7, cell division cycle associated 7; HELLS, helicase lymphoid specific; TET, ten-eleven translocation; ZBTB24, zinc-finger and BTB domain-containing 24.