This book features contributions from internationally renowned scientists from Europe and the USA covering aspects of immunoglobulin subclasses from a molecular and mechanistic approach. The first section presents a detailed discussion of the molecular structure and segmental flexibility of IgG subclasses, including how this controls their effector function. Structure-function relationships are fully developed in the second section by means of a functional approach to the study of complement activation and opsonization by IgG subclasses. The final section contains a generous account of the regulation of IgG subclass expressions.