Recombinant adenovirus (rAd) vectors have received considerable attention for gene therapy because of their high transduction efficiency. However, recombinant gene expression from rAd vectors elicits rapid and potent immune responses to foreign transgene products. Such immunogenicity limits the duration of transgene expression and poses a major challenge to the use of rAd vectors for gene therapy. In contrast, the inherent immunogenicity of these vectors is a desirable feature for vaccine development. The immunogenicity and protective efficacy of rAd vector-based vaccines have now been demonstrated in a number of animal models, and rAd vaccines for a variety of pathogens are currently being explored in early-phase clinical trials. In this review, we describe progress in the development of rAd vector-based vaccines with a focus on human immunodeficiency virus type 1.