ABSTRACT. The receptors for the Il-3/IL-5/GM-CSF cytokine family are composed of a heterodimeric complex of a cytokine-specific ␣ chain and a common  chain (c). Binding of IL-3/IL-5/GM-CSF to their respective receptors rapidly induces activation of multiple intracellular signalling pathways, including the Ras-Raf-ERK, the JAK/STAT, the phosphatidylinositol 3-kinase PKB, and the JNK/SAPK and p38 signalling pathways. This review focuses on recent advancements in understanding how these different signalling pathways are activated by IL-3/IL-5/GM-CSF receptors, and how the individual pathways contribute to the pleiotropic effects of IL-3/IL-5/GM-CSF on their target cells, including proliferation, differentiation, survival, and effector functions. cell signal 10;9:619-628, 1998.