The last half century has witnessed the birth, infancy, and early adolescence of a new field, intestinal immunology, with an explosion of knowledge about the role of the intestinal immune system in normal intestinal physiology and disease. This field is still in its rapid growth phase. A major spin-off of such growth will be the development of new approaches for the diagnosis and treatment of disease. For example, studies of oral tolerance have led to new insights into possible mechanisms of autoimmunity and ultimately could lead to new treatments for autoimmune disease. The discovery that Peyer's patches are a major inductive site for initiation of the mucosal immune response, and IgA responses in particular, and that antigen enters these sites via the M cell, forms one current basis for the development of new mucosal vaccines and vaccine delivery systems. Studies of immunogenetics are leading to new insights into the molecular basis of diseases such as celiac disease, IBD, and hepatic disorders. Studies of cytokines and the role they play in acute and chronic inflammation are leading to new approaches for the treatment of intestinal inflammatory diseases. The field of intestinal immunology is now well on its way through the turbulent "teenage" years. It is true maturation over the next several decades will test and witness the evolution and validity of concepts formed over the past 50 years. Certainly, tremendous growth and change will come with the increasing application of molecular tools, and the enthusiasm and the fresh insights brought by the next generation of young investigators, as they begin to further unravel the intricacies of the intestinal immune system and its role in health and disease.