Viral infections are a common cause for the development of cancer. Most common among the cancer-inducing viruses are human papillomaviruses, which cause cervical cancer among other things. Cancer viruses aim to keep their host cells alive and simultaneously use their oncogenes to interfere with cellular phenomena such as proliferation and programmed cell death. The most effective way of preventing viral cancers is to reduce the frequency of cancer virus infections by using vaccinations and by intervening in high-risk behavior. In addition, the infections must be detected and treated in advance of cancer development.