Colonoscopy is the mainstay diagnostic modality to assess a variety of gastrointestinal symptoms, as well as screen for premalignant and malignant lesions of the colon. In addition to allowing diagnostic accuracy, colonoscopy allows direct therapy for a variety of conditions, most notably endoscopic control of gastrointestinal bleeding and removal of premalignant lesions. This atlas serves to instruct medical students, and medical and surgical housestaff on commonly encountered colonoscopic findings and disorders, by providing typical colonoscopic photographs of these conditions, along with a brief narrative description of the findings.