Recombinant adenoviral vectors have served as one of the most efficient gene delivery vehicles in vivo thus far. Multiply attenuated or completely gutless adenoviral vectors have been developed to achieve long-term gene expression in animal models by overcoming cellular immunity against de novo synthesized adenoviral proteins. However, since adenovirus lacks native integration machinery, the goal of gene therapy obtaining permanent expression cannot be realized with current adenoviral vector systems. Recent studies have shown that replication-incompetent adenoviral vectors randomly integrate into host chromosomes at frequencies of 0.001-1% of infected cells. To improve the integration frequencies of adenoviral vectors, a variety of hybrid vectors combining the highly efficient DNA delivery of adenovirus with the integrating machinery of retroviruses, adeno-associated viruses, and transposons, have been emerging. These hybrid vectors have shown promise, at least in in vitro systems. Furthermore, adenoviral vectors have shown potential as gene targeting vectors. These developments should eventually lead to more effective gene therapy vectors that can transduce a myriad of cell types stably in vivo.