Biochemical, epigenetic, genetic, and imaging biomarkers are used to identify people at high risk for developing cancer. In cancer epidemiology, epigenetic biomarkers offer advantages over other types of biomarkers because they are expressed against a person's genetic background and environmental exposure, and because epigenetic events occur early in cancer development. This chapter describes epigenetic biomarkers that are being used to study the epidemiology of different types of cancer. Because epigenetic alterations can be reversed by chemicals and activate gene expression, epigenetic biomarkers potentially have numerous clinical applications in cancer intervention and treatment and significant implications in public health. This review discusses cancer biomarkers, the characteristics of an ideal biomarker for cancer, and technologies for biomarker detection.