RNA silencing, which is termed post-transcriptional gene silencing in plants, is an RNA degradation process through sequence-specific nucleotide interactions induced by double-stranded RNA. In plants, RNA silencing not only serves as a component of the defense mechanism, but also participates in the regulation of endogenous gene expression in a variety of developmental processes. This review elaborates the current progress on the understanding of the molecular basis of RNA silencing including a mechanistic link between the regulation of microRNA and RNA silencing. The practical use of RNA silencing as a reverse genetics approach in plant functional genomics is also discussed.