RNA interference (RNAi) is a post-transcriptional gene-silencing phenomenon induced by double-stranded RNA. It has been widely used as a knockdown technology to analyze gene function in various organisms. Although RNAi was first discovered in worms, related phenomena such as post-transcriptional gene silencing and coat protein mediated protection from viral infection had been observed in plants prior to this. In plants, RNAi is often achieved through transgenes that produce hairpin RNA. For genetic improvement of crop plants, RNAi has advantages over antisense-mediated gene silencing and co-suppression, in terms of its efficiency and stability. It also offers advantages over mutation-based reverse genetics in its ability to suppress transgene expression in multigene families in a regulated manner.