Endoscopy has assumed a preeminent role in the diagnostic approach to IBD. It is more sensitive than radiography in detecting early, subtle changes of IBD, both through endoscopic appearance and histologic sampling of mucosa. Endoscopy also appears to be a safe technique in patients presenting with severe forms of colitis and can play an important role in defining the etiologic basis of disease in this subgroup of patients. In addition to its diagnostic role, endoscopy has proven useful in surveying disease activity, through the development of endoscopic disease activity indices. Endoscopy has also found a prominent role in the diagnostic and therapeutic approach to IBD complications. Endoscopic surveillance of chronic UC patients at risk for colon carcinoma has helped to define a therapeutic approach to this serious complication of UC. Endoscopic therapy has been applied to treat stricture formation associated with long-standing CD. Biliary endoscopy also represents the strategy of choice for diagnosing primary sclerosing cholangitis, an extraintestinal complication occurring in 5% of UC patients. Finally, endoscopy may help facilitate the discovery of disease pathogenesis in IBD, through the use of endoscopically recovered biopsy specimens in the research laboratory. Endoscopy allows for ready access to human tissue that has been the cornerstone of disease-related research over the past two decades.