In recent years, we have witnessed the discovery of a new mechanism of gene regulation called RNA interference (RNAi), which has revitalized interest in the development of nucleic acid-based technologies for therapeutic gene suppression. This review focuses on the potential therapeutic use of RNAi, discussing the theoretical advantages of RNAi-based therapeutics over previous technologies as well as the challenges involved in developing RNAi for clinical use. Also reviewed, are the in vivo proof-of principle experiments that provide the preclinical justification for the continued development of RNAi-based therapeutics.