A colonoscope is a long, flexible instrument fitted with a camera and light, used to examine the interior of the colon. Passed through the rectum, it lets the physician inspect the bowel lining directly, take biopsies, and remove polyps during the same procedure, making it both diagnostic and therapeutic. Colonoscopy is the gold standard for colorectal cancer screening and investigation of bleeding, persistent bowel changes, and inflammatory bowel disease. Preparation requires thorough bowel cleansing with laxative drinks and a low-residue diet beforehand. The instrument’s ability to prevent cancer by removing precancerous polyps makes it uniquely valuable.