Adenoviruses contain genes that have evolved to control the host immune and inflammatory responses; however, it is not clear whether these genes function primarily to facilitate survival of the virus during acute infection or during its persistent phase. These issues have assumed greater importance as the use of adenoviruses as vectors for gene therapy has been expanded. This review will focus on the mechanism of immune evasion mediated by the proteins encoded within the early region 3 (E3) transcription region, which affect the functions of a number of cell surface receptors including Fas, intracellular cell signaling events involving NF-κB, and the secretion of pro-inflammatory molecules such as chemokines. The successful use of E3 genes in facilitating allogeneic transplantation and in preventing autoimmune diabetes in several transgenic mouse models will also be described.