With the completion of the Human Genome Project, there is an increasing, substantial need to apply RNA silencing technologies to post-genome research. In this review, we focus on three silencing technologies: antisense, RNA interference, and ribozymes. These RNA silencing approaches are designed to specifically block gene expression, and have applications in investigations of gene function, pharmacogenetics and pharmacogenomics, and identification of novel targets for therapy. With high specificity and affinity, oligonucleotide therapeutic agents are being developed as novel treatments for various diseases such as cancer, cardiovascular diseases and infectious diseases. These drugs can be used alone or in combination with current treatment strategies including chemotherapy or radiation therapy. However, the potential of these therapeutic agents based on RNA silencing technologies has not yet been fully realized, and further investigations are needed to define their specificity and efficacy, especially in the clinical setting.