RNA interference (RNAi) is the phenomenon of gene silencing by double-stranded RNA (dsRNA) at transcriptional and post-transcriptional levels in a sequence-specific manner. Reverse genetic approaches using RNA interference (RNAi) have become a major tool for biological researches since its discovery in the nematode Caenorhabditis elegans. In this review, we overview how the RNAi phenomenon was discovered and how the underlying mechanism has been elucidated. We also describe and discuss how RNAi experiments can be performed and how RNAi can be used for genetic studies.