Viruses that produce tumors are defined as oncogenic viruses. These include: Papovaviridae; Papillomavirus (some); Herpesviridae Lymphocryptovirus (Epstein-Barr virus); Hepadnavirus; Hepatitis B virus(HBV); Adenoviridae; Poxviridae; Human T-cell leukaemia virus (HTLV-1; HTLV-2); Sarcoma viruses of cats, chickens, rodents; Mammary tumor virus of mice and Feline leukaemia virus (FeLV).This book presents the latest research in this field.