Polymorphonuclear neutrophils, monocytes, and macrophages have numerous important functions in immunity, particularly the ingestion of antibody-coated microorganisms and cells. This review focuses on recent progress in the understanding of the family of receptors for the Fc end of IgG (Fc-[gamma] R) on these phagocytes. The control of Fc [gamma] R expression, the cellular output signals from receptor engagement, and the basis of immediate and downstream signals in phagocyte activation are reviewed. Mice are increasingly being used in transgenic and knockout models of Fc [gamma] R biology. Relevant differences in the Fc [gamma] R endowments of mice and humans are detailed.