Recombinant adeno-associated virus vectors have been shown to safely transduce a number of tissues in preclinical animal studies. The level of gene transfer is sufficient to successfully treat a large number of medical disorders. Moreover, the long-term persistence of the vector sequences in animals makes it likely that this vector will be useful for genetic diseases requiring life-long therapy. This review outlines the biological principles of the vector, as well as its advantages and current limitations as it relates to use in hepatic gene therapy.