The effector functions of immunoglobulins of the G class (IgGs) are essential for their effective use in therapy. The functions that operate following complex formation with cognate antigen involve binding to C1q (to mediate complement fixation) and the Fc receptors, Fc gamma RI, II and III. Another class of functions that is independent of antigen binding encompasses the transfer of antibodies across the placenta and maintaining the levels in the serum. All effector functions of IgGs are conferred by sequences in the Fc region of antibodies, and this review discusses the localisation of the functions to specific amino acid residues. Such knowledge is of use for the further improvement of IgCs for therapy.