Inflammatory Bowel Disease (IBD) is a general term used for two chronic inflammatory conditions of the gastrointestinal tract: Ulcerative Colitis and Crohn's Disease. While there are some similarities between the two diseases, there are important differences between the two.

The etiology, or cause, of IBD is unknown but likely involves genetic and immunologic components affecting the body's ability to differentiate between the gastrointestinal tract and foreign entities. The course of IBD is unpredictable and can be characterized by periods of active disease (exacerbations or "flare-ups") and periods of remission, both of unknown duration and frequency. Individual experiences with the disease can also be quite varied; some experiencing mild symptoms that respond readily to medications and nutritional interventions, and others who will experience significant difficulties requiring intensive medical management, hospitalization and surgery.

Usually, clinicians are able to differentiate between Crohn's Disease and Ulcerative Colitis (using biopsy and pathology to assist with the diagnosis). However, in about 15 per cent of IBD cases, differentiation and definitive diagnosis may not be feasible, and the subsequent diagnosis may be that of "indeterminant colitis".