Malignant gliomas are devastating diseases that localize within the central nervous system and are notoriously invasive. Despite recent advances in established treatment modalities such as postoperative radiotherapy and chemotherapy for gliomas, no definitive improvement in survival has been observed. However, progress in the understanding of the biology of these tumors allows for the development of translational research projects and new therapeutic approaches such as gene therapy. One of the most recent strategies is based on the use of targeted oncolytic adenoviruses. The progress of the oncolytic adenoviral system relies on the knowledge of the molecular biology of both the adenovirus and cancer. This review outlines the main strategies currently used to improve adenoviral infection, to restrict adenoviral replication to tumor cells, and to optimize the anticancer effect of oncolytic adenoviruses. Specifically, we discuss the concepts of conditionally replicative adenoviruses, tropism modifications used to efficiently redirect infectivity to cancer cells, and the transcription/transduction systems that limit the adenovirus to the target host cell. Mastery of the mechanisms of adenoviral infection and replication will lead to a full realization of the potential for adenoviruses as critical anticancer tools, and may result in the improvement of the prognosis of patients with brain tumors.