Mast cells are important effector cells in allergic inflammatory reactions. The aggregation of the high-affinity IgE receptor (Fc epsilon RI) on the surface of mast cells initiates a complex cascade of signaling events that ultimately leads to the release of various mediators involved in allergic inflammation and anaphylactic reactions. The release of these mediators is tightly controlled by signaling pathways that are propagated through the cell by specific phosphorylation and dephosphorylation events. These events are controlled by protein kinases and protein phosphatases which either positively or negatively regulate the propagation of the signal through the cell. This review summarizes the role of both positive and negative regulators of Fc?RI-induced mast cell activation.