The past few years have seen a wider acceptance of a role for DNA methylation in cancer. This can be attributed to three developments. First, the documentation of the over-representation of mutations at CpG dinucleotides has convincingly implicated DNA methylation in the generation of oncogenic point mutations. The second important advance has been the demonstration of epigenetic silencing of tumor suppressor genes by DNA methylation. The third development has been the utilization of experimental methods to manipulate DNA methylation levels. These studies demonstrate that DNA methylation changes in cancer cells are not mere by-products of malignant transformation, but can play an instrumental role in the cancer process. It seems clear that DNA methylation plays a variety of roles in different cancer types and probably at different stages of oncogenesis. DNA methylation is intricately involved in a wide diversity of cellular processes. Likewise, it appears to exert its influence on the cancer process through a diverse array of mechanisms. It is our task not only to identify these mechanisms, but to determine their relative importance for each stage and type of cancer. Our hope then will be to translate that knowledge into clinical applications.