Wounded plants emit complex blends of volatile organic compounds that can alter the physiology of nearby plants, yet the identity of the active signals and the mechanisms by which they are perceived remain poorly understood. Here, we show that volatiles released from wounded maize plants induce defense responses in unwounded neighbors. To identify the active components, we used mutant emitter lines lacking specific volatile biosynthetic enzymes, resulting in the selective loss of individual compounds or compound classes. Using this approach, we show that green leaf volatiles (GLVs), a class of fatty acid-derived C6 aldehydes, alcohols, and esters that are rapidly induced by wounding, are both necessary and sufficient to induce defense responses in neighboring plants. Furthermore, we identify two homologous membrane-localized receptors that bind the GLVs cis-3-hexenol and cis-3-hexenyl acetate with high affinity and specificity. Loss of these receptors abolishes maize responsiveness to GLVs. Accordingly, receptor mutants are no longer able to detect and respond to herbivore-attacked neighbors. Forty years after the discovery of “talking trees,” these findings provide a molecular mechanism for plant volatile perception and demonstrate how plants can detect herbivory by sensing wound-induced volatiles through specific extracellular receptors.