DNA Methyltransferases are important enzymes in a broad range of organisms. Dysfunction of DNA methyltransferases in humans can lead to cancer and other severe diseases. The book describes the enzymes and their mechanisms in bacteria, humans and plants and also explains the biological role of DNA methylation, functioning as an essential epigenetic mark. In addition, the book discusses the role of DNA methylation in diseases, including the contribution of mutations in DNA methyltransferases to cancer; it explains targeted rewriting of DNA methylation by designed DNA methyltransferases, as well as the biological role and enzymatic processes of DNA demethylation. Furthermore, the book summarizes recent methods for the analysis of DNA methylation in human DNA. The book represents a comprehensive state-of-the-art- work and is a must-have for advanced researchers in the field of DNA methylation and epigenetics.