Here is an up-to-date review of important new methods and results in anti- idiotypes, receptors, and molecular mimicry. It begins with a discussion of the theoretical background of the anti-idiotypic network, it's role in the regulation of immune response, and the physical characteristics of anti- idiotypic antibodies. It then goes on to explore many exciting applications in such areas as insulin action, thyroid cell function, the neurosciences, cardiology, virology, pharmacology, and reproduction.