The past decade has witnessed a tremendous increase in our understanding of the role of ethylene in plant development. Genes encoding enzymes of the ethylene biosynthesis pathway have been isolated, allowing the manipulation of endogenous ethylene levels in intact plants. In parallel, a collection of ethylene mutants was obtained by using a simple response assay. This resulted in the identification of several genes involved in ethylene signal transduction. The data obtained using these new tools have allowed long-standing hypotheses to be tested, while gaining novel insight into the function of ethylene in development. Recent molecular evidence supported the existence of an intense hormonal cross-talk during plant growth. Numerous processes are controlled by ethylene in a close interaction with auxin, and often it was impossible to differentiate between auxin and ethylene effects. Molecular-genetic tools are now allowing the dissection of these interactions. Ethylene does not seem essential for many developmental processes. Nevertheless, it is of crucial importance for survival in most species as it occupies a key position in the developmental response mechanisms of plants under mechanical stress.