Transposons have been successfully exploited as insertional mutagens for the efficient identification and isolation of genes (transposon tagging) in many organisms. Plants are no exception. The maize Activator and Suppressor-mutator transposons function when transferred into heterologous plant species, and many different gene tagging systems have been developed. These systems have recently been used to clone novel and important genes, including disease resistance loci from Nicotiana tabacum, tomato and flax.