Approximately 15 per cent of human cancer incidence can be attributed to virus infection, i.e. viruses represent the second most important risk factor (after tobacco consumption) for cancer development in humans. Today, five virus types are known to be involved in causing human cancer: papillomaviruses, retroviruses, herpesviruses, hepadnaviruses, and flaviviruses. This volume of "Monographs in Virology" provides a comprehensive review of a number of DNA tumor viruses. Leading experts in the field of tumor virology discuss up-to-date information, focusing on the transforming genes of DNA tumor viruses, the mechanisms of transformation and the in vitro methodology used for their identification and characterization. Even though DNA tumor viruses are a diverse group, in vitro studies have revealed several common mechanisms of viral transformation. The individual chapters of the book describe the latest research on the identification of viral oncogenes and their targets.