This chapter discusses the evolutionary implications of DNA methylation. DNA methylation is a covalent modification that alters the chemical identity of DNA and regulates gene expression, providing a mechanism for cell type–specific gene expression programs in complex multicellular organisms, as well as increased genomic plasticity and adaptability. This adaptability has been fundamental to evolutionary processes, enhancing organismal fitness through improved responses to environmental changes. DNA methylation is established post-replication by DNA methyltransferases (DNMTs), which transfer methyl groups to cytosine or adenine bases. In bacteria, these modifications occur at specific sequences, enabling faithful restoration of methylation patterns after cell division. In vertebrates, methylation predominantly targets CG dinucleotides, with maintenance enzymes ensuring semiconservative inheritance of these patterns during replication. The persistence of DNA methylation patterns through cell divisions raises questions about their potential role as an independent mechanism in evolution and speciation, beyond genetic variation alone. Furthermore, environmental and social cues can influence DNA methylation, echoing Lamarckian ideas of environmentally directed evolution, though factors such as the erasure of methylation during gametogenesis and the association of DNA methylation variation with genetic sequence variation remain challenges. Synthetic theories suggest that DNA methylation may drive phenotypic diversity that is later genetically fixed. While it remains uncertain whether DNA methylation directly causes permanent evolutionary change, its emergence has undeniably expanded the range of phenotypes from identical genetic sequences, significantly enhancing adaptability, fitness, and the evolutionary potential of species.