RNA interference (RNAi) represents a promising new gene silencing technology for functional genomics and a potential therapeutic strategy for a variety of genetic diseases. RNAi involves the targeted post-transcriptional degradation of messenger RNA thereby inhibiting the synthesis of the desired protein. This effectively leads to silencing of gene expression. The effectors of this process are short interfering RNA (siRNA) duplexes (approximately 21-23nt) that are key intermediaries in the specific degradation of target mRNA following incorporation into the RNA-induced silencing complex (RISC) in the cytosol. However, due to the large molecular weight and negative charge of siRNA duplexes the effective cellular uptake and intracellular delivery appear to represent a major challenge for the widespread use of RNAi in vivo. This review summarises some of the main delivery strategies that have been attempted for the transfection of siRNA to cells in vitro and in vivo.

RNA interference (RNAi) is a natural cellular process that effects post-transcriptional gene silencing in eukaryotic systems. Small interfering RNA (siRNA) molecules are the key intermediaries in this process which when exogenously administered can inhibit or "silence" the expression of any given target gene. Thus, siRNA molecules hold great promise as biological tools and as potential therapeutic agents for targeted inhibition of disease-causing genes. However, key challenges to the effective and widespread use of these polyanionic, macromolecular duplexes of RNA are their appropriate design and efficient delivery to cells in vitro and in vivo. This review highlights the current strategies used in the design of effective siRNA molecules and also summarises the main strategies being considered for the exogenous delivery of siRNA for both in vitro and in vivo applications.