RNA interference (RNAi) is a process of double-stranded RNA-dependent post-transciptional gene silencing that occurs mainly in the mRNA processing bodies (P-bodies) of cells. It has become the most powerful and widely used gene strategy for genetic analysis and molecular therapeutics, based on the highly specific and efficient silencing of target genes. The key challenge for achieving effective RNAi in vitro and in vivo is its delivery to the desired organs and into the target cells. The RNAi delivery systems can be either non-viral or viral vectors. The main candidate for RNAi as a therapeutical tool is the viral-based vectors, including retroviruses, adenoviruses, adeno-associated viruses (AAV), lentiviruses and herpes simplex virus-1 (HSV-1). There is a high potential for clinical use of RNAi in treatment of a wide variety of human diseases, including genetic disorders, infectious diseases and cancer. This paper reviews the designs of inducible, tissue specific, hybrid, oncolytic and high-throughput RNAi vectors based on plasmids or viruses, and discusses their specificity, efficiency and safety.