DNA hypermethylation of CpG islands plays an important role in gene regulation during cancer development. Many techniques have been developed to detect global DNA methylation in cancer cells compared to normal tissues. This knowledge helps us to better understand cancer progression and also aids in the development of new biomarker for early cancer detection. New prognostic tools for monitoring drug efficacy during cancer treatment can also be developed. In this review, we will examine the different techniques that have been used to study DNA methylation, as well as the emerging high resolution, high throughput techniques for identification of methylated regions to defining cancer related genes in the cancer methylome.