Epigenetics is the study of heritable changes in gene expression, which does not arise due to changes in the DNA sequence. Epigenetic alterations include micro-satellite instability, histone modifications and DNA methylation. DNA methylation is a normal phenomenon in eukaryotic cells and occurs across the whole genome. Methylation target cytosine-residues followed by a guanine on the DNA strand (called CpG-islands) converting these to methyl-cytosine. Un-methylated CpG-islands exist in a high concentration in the promoter regions of human genes, and DNA promoter hypermethylation leads to decreased transcriptional activity. This event happens in tumour suppressors leading to gene silencing which is related to tumour genesis. CpG-Island hypermethylation is shown to be a non-random process and the pattern of gene hypermethylation appears to be specific to individual cancers. This lead to the definition of a CpG-Island Methylator Phenotype (CIMP) in CRC, a panel of genes being hypermethylated in CRC tumours, and there is a growing body of literature on the correlation between hypermethylated genes and CRC. This investigation has primarily focused on DNA obtained from CRC biopsies but in recent years focus has moved to hypermethylated DNA obtained from blood and stool samples.