During the past decade, molecular genetic studies on the reference plant Arabidopsis have established a largely linear signal transduction pathway for the response to ethylene gas. The biochemical modes of action of many of the signaling components are still unresolved. During the past year, however, progress in several areas has been made on several fronts. The different approaches used have included a functional study of the activity of the receptor His kinase, the determination of the ethylene receptor signaling complex at the endoplasmic reticulum and of the regulation of CONSTITUTIVE TRIPLE RESPONSE1 (CTR1) activity by these receptors, the identification of a unique MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) cascade, the cloning and characterization of numerous ETHYLENE INSENSITIVE3 (EIN3)/EIN3-like (EIL) transcription factors from many plant species, and the integration of the ethylene and jasmonate response pathways via the ETHYLENE RESPONSE FACTOR (ERF) family of transcription factors. The elucidation of the biochemical mechanisms of ethylene signal transduction and the identification of new components in the ethylene response pathway in Arabidopsis are providing a framework for understanding how all plants sense and respond to ethylene.