Posttranslational modifications to histones affect chromatin structure and function resulting in altered gene expression and changes in cell behavior. Aberrant gene expression and altered epigenomic patterns are major features of cancer. Epigenetic changes including histone acetylation, histone methylation, and DNA methylation are now thought to play important roles in the onset and progression of cancer in numerous tumor types. Indeed dysregulated epigenetic modifications, especially in early neoplastic development, may be just as significant as genetic mutations in driving cancer development and growth. The reversal of aberrant epigenetic changes has therefore emerged as a potential strategy for the treatment of cancer. A number of compounds targeting enzymes that regulate histone acetylation, histone methylation, and DNA methylation have been developed as epigenetic therapies, with some demonstrating efficacy in hematological malignancies and solid tumors. This review highlights the roles of epigenetic modifications to histones and DNA in tumorigenesis and emerging epigenetic therapies being developed for the treatment of cancer.