For successful gene vaccination and therapy of cancer, it is essential to develop gene delivery vectors that can meet clinical and social requirements. The need for improved vectors was clearly manifested during the peak of the first wave of gene therapy. Adenoviral (Ad) vectors have recently drawn the attention of many of those involved in the field of gene therapy for cancer because of their practical advantages and application potential. Many experiments, innovations, preclinical studies, and clinical trials have generated an overwhelming amount of data and literature concerning this vector system. It is hoped that the comprehensive review presented here, which includes the principles, potential, capacity, and limitations of the current Ad systems, will help to further the rational development of the system. The literature in this article is organized in an attempt to emphasize Ad vector development in the aspects of technical approaches, practical hurdles and strategies to overcome them, significant experimental results, recent advances, future directions, etc. The technical range of this review covers details that are intended to serve as a reference for advanced technical readers and provide a foundation for initiates in the field of Ad vector gene therapy. The material presented here is also intended for nontechnical persons who want to have an overview of the significance and potential of the technology.