"The Principles & Protocols Series" is designed for upper level undergraduates, postgraduates and researchers, particularly those new to a field. Books in the series outline the theoretical background to experimental approaches, followed by bullet-point protocols, which are generic and can be adapted for particular systems. RNA interference (RNAi) has been one of the most exciting and significant new methodologies to appear in the past decade, and it now finds widespread application. This methods manual provides an introduction to the phenomenon to RNA Interference and specific protocols for RNAi, in organisms from plants and C.elegans to Drosophila and mammals. Also included are chapters covering small hairpin RNAs and viral-induced gene silencing.