Despite considerable advances in our understanding of cancer biology, early diagnosis of colorectal cancer remains elusive. Based on the adenoma-carcinoma sequence, cancer develops through the progressive accumulation of mutations in key genes that regulate cell growth. However, recent mathematical modelling suggests that some of these genetic events occur prior to the development of any discernible histological abnormality. Cells acquire pro-tumourigenic mutations that are not able to produce morphological change but predispose to cancer formation. These cells can grow to form large patches of mucosa from which a cancer arises. This process has been termed “field cancerisation”. It has received little attention in the scientific literature until recently. Several studies have now demonstrated cellular, genetic and epigenetic alterations in the macroscopically normal mucosa of colorectal cancer patients. In some reports, these changes were effectively utilised to identify patients with a neoplastic lesion suggesting potential application in the clinical setting. In this article, we present the scientific evidence to support field cancerisation in colorectal cancer and discuss important limitations that require further investigation. Characterisation of the field defect is necessary to enable early diagnosis of colorectal cancer and identify molecular targets for chemoprevention. Field cancerisation offers a promising prospect for experimental cancer research and has potential to improve patient outcomes in the clinical setting. Despite due advances in our understanding of cancer biology, early diagnosis of colorectal cancer remains elusive. Based on the adenoma-carcinoma sequence, cancer develops through the progressive accumulation of mutations in key genes that regulate cell growth. However, recent mathematical mode suggests that some of these genetic events occur prior to the development of any discernible histological abnormality. Cells acquire pro-tumourigenic mutations that are not able to produce morphological change but predispose to cancer formation. These cells can grow to form large patches of mucosa from which a cancer arises Several has have little experience in the scientific literature until recently. Several studies have now demonstrated rendered cellular, genetic and epigenetic alterations in the macroscopically normal mucosa of colorectal cancer patients. In some reports, these changes were effectively utilized to identify patients wi th a neoplastic lesion suggesting potential application in the clinical setting. In this article, we present the scientific evidence to support field cancerisation in colorectal cancer and discuss important downs that require further investigation. Characterization of the field defect is necessary to enable early diagnosis of colorectal cancer and identify molecular targets for chemoprevention. Field cancerisation offers a promising prospect for experimental cancer research and has potential to improve patient outcomes in the clinical setting.