A wide stream of in vivo studies have now confirmed the prediction that rAAV vectors have the primary requirements for effective gene transfer. AAV vectors can efficiently transduce both dividing and non-dividing cells, they are able to mediate long-term gene expression, and are showing no signs of cytotoxicity or immune response. In addition, recent advancements in the production and purification technologies of AAV vectors have lead to the ability to generate high titer clinical grade vector. This review will focus on studies which have fueled the emergence of AAV as an attractive vector for gene delivery. Discussion will center on the ability of AAV to mediate long-term transgene expression in vivo, the recent success of AAV vectors in animal models, and current clinical trials that... are testing rAAV vectors for the treatment of cystic fibrosis.