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FcγRIIa functions as an amplifier of αIIbβ3-mediated outside-in signaling in platelets. A platelet is shown schematically both en face and in transverse section and depicts numerous copies of the major platelet integrin, αIIbβ3, surrounding occasional FcγRIIa receptors. Binding to multivalent fibrinogen molecules leads to crosslinking of adjacent αIIbβ3 receptors, bringing their cytoplasmic domains and associated Src-family kinases into close proximity, where they become transphosphorylated and activated. Eventual tyrosine phosphorylation of FcγRIIA tyrosine residues leads to recruitment of Syk kinase and transmission of outside-in activation signals. Illustration by Peter Newman and Jan Harris. See the article by Zhi et al on page 1858.