The term "epigenetics" is defined as "heritable changes in gene expression that occur without changes in DNA sequence". Recently, it has been revealed that DNA methylation and histone modifications such as acetylation, methylation and phosphorylation are epigenetic mechanisms according to this definition. In other words, these posttranslational modifications are important factors in determining when and where a gene will be expressed. To date, several enzymes that catalyze DNA or histone modifications have been identified, such as DNA methyltransferases and histone deacetylases. Inhibitors and activators of enzymes controlling epigenetic modifications are considered useful not only as tools for the elucidation of cellular and biological phenomena, but also as therapeutic agents, since disruption of the balance of epigenetic networks is known to cause some disease states such as cancer. In this review, we present natural products and synthetic molecules that inhibit or activate enzymes catalyzing DNA methylation or histone modifications, and discuss the potential of epigenetic therapy.