An aberrant crypt foci (ACF) obtained from the proximal (right) colon shows a distinct serrated morphology similar to that observed in human serrated adenomas (cover image). ACF are considered to represent the earliest macroscopically identifiable abnormality within the colorectal mucosa and can be routinely identified during high-definition chromoendoscopy. Importantly, these small lesions often harbor somatic mutations to colorectal cancer-associated oncogenes, including activating mutations to KRAS and BRAF. Furthermore, ACF provide valuable insight into the earliest stages of colorectal carcinogenesis andmay serve as a surrogate marker of future cancer risk. For more information, see the article by Drew and colleagues on page 823.