Oncogenesis is a multifactorial process that normal cells gain divergent properties that allows them to multiply without regulation, invade tissues, and ultimately metastasize. A combination of genetic and epigenetic factors is involved in this process. The concept of tumor viruses was born decades ago when Epstein-Barr virus was discovered in patients with Burkitt’s lymphoma. Since then, several other viruses have been discovered to have oncogenic properties. It is estimated that about 20% of all cancer cases globally are attributable to viral infections. It is important to study these viruses as they are considered preventable causes of cancer. Viruses are known to use several mechanisms to induce cancer such as inducing genomic instability, increasing cellular proliferation, avoiding apoptosis, altering innate DNA repair mechanisms, and changing cellular polarity. Discovering underlying mechanisms used by these viruses to cause cancer can help find effective therapies for cancer prevention and treatment. Antiviral therapy has significantly decreased cancer rates in infected patients in recent years. Novel targeted therapies that aim at mechanisms utilized by viruses are potential treatments for cancers attributable to viruses. In this chapter, we discuss the oncogenic viruses, different types of cancers they generate, the underlying mechanisms that result in cancer, and preventative and therapeutic options currently available for these cancers.