The effects of ethylene and ethylene signal transduction have been long studied in plants. It was only recently reported that a single-celled cyanobacterium, Synechocystis, contains a functional ethylene receptor. However, it remains to be determined if functional ethylene receptors are more widespread. This review summarizes what is known about responses to ethylene, ethylene receptors, and signal transduction in non-plant species. A summary is provided of information gleaned from searches of sequenced genomes and the possibility that ethylene receptors are widespread in microbes is discussed.