Immunoglobulin E (IgE) plays a central role in the pathogenesis of allergic diseases by interacting with two membrane receptors: high-affinity FcepsilonRI and low-affinity FcepsilonRII (CD23). Allergeninduced IgE-occupied FcepsilonRI aggregation on the mast cell or basophil cell surface leads to the activation of intracellular signaling events and eventually the release of pre-formed and de novo synthesized inflammatory mediators. The role of FcepsilonRII in allergic diseases has been proposed to include regulation of IgE synthesis, enhanced histamine release from basophils, and a contribution to Ag-IgE complex presentation but the exact function of CD23 remains poorly understood. This review summarizes some new developments in IgE Fc-receptor studies with an emphasis on regulation of FcepsilonRI expression and signal transduction, including monomeric IgE, lipid raft segregation, and some recently identified negative regulators. A better understanding of signaling events following IgE FcR aggregation will shed new light on how allergy patients might be treated more safely and effectively.