This thesis presents the latest ideas and discoveries on the evolution and origin of the viruses. Viruses, as abundant biological entities that are infecting all forms of life known today, are very complex and diverse. Thus, their evolutionary processes are still unclear and complex, and their origin is very diverse. The three main hypotheses of viral origin are progressive, or escape hypothesis, regressive or hypothesis of reduction and, the virus first hypothesis. Because of their wide variety, biologists have been struggling to classify viruses and associate them within the conventional tree of life. The viral genomes of the three domains of cellular life (bacteria, archaea, and eukaryotes) are significantly different. With numerous phylogenetic analyses of different classes of viruses, the evolutionary processes of these elements are becoming clearer and thus provide a better insight into this unique and still quite mysterious world.