Prevalent and often intractable diseases such as allergy, autoimmune disease, and many chronic inflammatory conditions can all be viewed as abrogation of normal immune function, especially of immune tolerance. As the understanding of the role and also of the mechanisms of immune tolerance is growing, so the potential for orally manipulating immune response to either prevent the loss or to re-establish tolerance can be viewed as a new and exciting intervention. Stimulation of the correct response to re-balance the immune system can be achieved by orally feeding the appropriate antigen, or by any mechanism, e.g probiotic bacteria, which selectively down-regulates either the Th1 or Th2 bias and their respective promoting cytokines and up regulates the Th3 dominance. In-vitro, animal, and human studies aimed at stimulating oral tolerance are beginning to produce compelling evidence of the value of this type of intervention in preventing or treating many common immune based disorders. Current evidence of the effectiveness, safety and practicality of this of this approach will be presented, together with an evaluation of future prospects of this unique type of immunotherapy.