RNA interference (RNAi) is a form of gene silencing induced by double stranded RNA (dsRNA) that is processed into short interfering RNAs (siRNAs). RNAi can induce both post-transcriptional and transcriptional gene silencing. In Caenorhabditis elegans, there are several distinct pathways where post-transcriptional or/and transcriptional RNAi mechanisms are involved. RNAi in C. elegans is also systemic and heritable. This review will discuss RNAi related pathways, features of RNAi in C. elegans and possibilities of endogenous gene regulation by RNAi.