The papers assembled in this volume bring the reader to the forefront of research on the third component of complement, one of the most versatile and multifunctional molecules known to date. Unlike publications on individual characteristics, this vollume brings together all the structural and functional aspects of C3 and the C3-binding proteins, the latter including serum proteins, cell surface receptors and proteins of foreign origin. A wealth of information on the various aspects of the genetics, chemistry, biology and pathophysiology of C3 and of the 20 different proteins described to date to react with C3 is presented in numerous concise and comprehensive reviews.