DNA methylation plays a pivotal role during development and carcinogenesis and is central to gene silencing. The recent characterization of the DNA methyltransferases Dnmt- and their protein partners have helped to understand the molecular basis underlying methylation-mediated gene silencing and its involvment in cancer, These discoveries have important implications to the comprehension of transcriptional regulation but also to understand the molecular basis underlying tumorigenesis. Moreover, these studies open new ways towards an epigenetic therapy of cancer.