A cutting-edge review of the important issues underlying the therapeutic use of nucleic acid-mediated gene silencing. Topics range from basic methodology and delivery to targeting and clinical targets. The authors thoroughly explain the latest developments in RNA biology, as well as the underpinnings of RNA interference, oligodeoxynucleotide delivery into cells, and strategies for targeting these molecules to accessible regions within the mRNA. They also provide some examples of how these new therapeutic compounds are being used clinically.