A long time ago, my teacher Michael Heidelberger described the study of com- plement as a black art. Since then, the introduction of chemical methods has opened the way to precise and objective investigation of the complement system, transmuting alchemy to science. The individual components of complement have been isolated in reasonably pure form, their intricate interactions have been unraveled, and their manifold activities as mediators of immunity and allergy have been delineated. These advances derive from the efforts of numerous investi- gators in many countries and were facilitated through the vast expansion of support of biomedical research during the past two decades. Today, complement is no longer a laboratory curiosity but represents a subject of intense interest to many students of biology and medicine. Numerous immunology books have been published in recent years, reflecting the rapid growth of this field, but the present work occupies a unique position as the only comprehensive modern text on complement. By integrating the chemical and biological aspects of the subject, and through craftmanship of a high order, this readable text offers much to the expert as well as beginner. Its broad coverage, clarity and thorough bibliographies make it a valuable source on the diverse activities of complement, including those mediated by the properdin pathway. As immunologists continue their search for better means of controlling microbial infections, allergic disorders, autoimmune diseases, and rejection of transplants, this impressive book will play its part toward achievement of these goals.