The viruses which have DNA as their genetic material and replicate using a DNA-dependent DNA polymerase are known as DNA viruses. The DNA viruses which cause cancers among humans are known as DNA tumor viruses. These include the hepatitis B virus, Kaposi sarcoma herpes virus, human papillomavirus, Merkel cell polyomavirus and Epstein-Barr virus. DNA tumor viruses cause tumors in human beings and animals by transforming the infected host cells. These oncogenic viruses encode viral proteins that prevent cell death by deregulating the integrated framework of host cellular processes. These viruses typically impair two families of tumor suppressor proteins, namely, retinoblastoma proteins and tumor proteins p53. This book aims to shed light on some of the unexplored aspects of DNA tumor viruses. It will serve as a reference to a broad spectrum of readers. Experts and students actively engaged in the research on these viruses will find this book full of crucial and unexplored concepts.