Colonoscopy is an endoscopic examination in which an endoscope is introduced through the anus to explore all the colon, and sometimes the terminal ileum by cannulation of the ileo-cecal valve. Colonoscopy has both a diagnostic and therapeutic role. First, it allows the inspection and eventual biopsy of mucosal abnormalities, for example to confirm the diagnosis of inflammatory bowel disease (IBD), and to screen and surveil patients for colorectal cancer (CRC). Indeed, colonoscopy is the most sensitive examination to diagnose colorectal premalignant and malignant neoplasms. Second, it allows to diagnose and treat bleeding sources such as angioectasias, diverticula and ulcers. Third, it can be used to remove neoplastic premalignant (i.e., adenomas) or superficially invasive lesions, by using snare or dedicated knives for the endoscopic submucosal dissection (ESD).