The gaseous hormone ethylene induces diverse effects in plants throughout their life cycle. Ethylene response is regulated at multiple levels, from hormone synthesis and perception to signal transduction and transcriptional regulation. As more genes in the ethylene response pathway are cloned and characterized, they illustrate the precision with which signaling can be controlled. Wounding, pathogenic attack, flooding, fruit ripening, development, senescence, and ethylene treatment itself induce ethylene production. Ethylene binding to receptors with homology to two-component regulators triggers a kinase cascade that is propagated through the CTR1 Raf-like kinase and other components to the nucleus. Activation of the EIN3 family of nuclear proteins leads to induction of the relevant ethylene-responsive genes via other transcription factors, eliciting a response appropriate to the original stimulus.