The Epstein-Barr Virus (EBV), also known as Human Herpes Virus 4, has been identified and described as the etiological agent of infectious mononucleosis. It is the first human virus found to be implicated in oncogenesis. EBV is associated with a number of biologically diverse cancers, mainly lymphoproliferations of B-cell origin. With the development of basic research and clinical medicine, new ideas related to the pathogenesis and clinical aspects of EBV-associated diseases have arisen recently. A significant progress in the number of hematopoietic stem cell and solid organ transplantations performed worldwide, involving high-risk patients, has contributed to an increase in the development of EBV-associated malignant post-transplant lymphoproliferative disorders. In the stem cell transplant setting, a post-transplant lymphoproliferative disorder has, in most cases, the nature of a secondary cancer. Apart from post-transplant lymphoproliferative disorders, other types of lymphoproliferative disorders are recognized and presented in this book. The main aim of this book is to provide readers with an overview of the impact of EBV on parameters that contribute to the development of malignancy in immunocompromised patients, particularly in recipients of a solid organ or hematopoietic stem cell transplant. Also, current concepts and practices in the diagnosis, management and prevention of EBV-associated malignancies are highlighted, with special emphasis on transplant patients. The book is organized in two sections. The first section describes the oncogenic potential of the Epstein-Barr Virus along with a thorough appraisal of its role in nasopharyngeal carcinoma and B-cell lymphoma. This part is essential for situating EBV in the field of oncogenesis, and presenting the pivotal role of EBV in contemporary oncology and transplantology. This is followed by the second section, which answers some of the questions related to post-transplant lymphoproliferative disorders. The book is a comprehensive collection of papers that describe the active processes induced by EBV in oncogenesis. As we live in the world where transplantation science is making rapid progress, the book is focused mostly on post-transplant lymphoproliferative disorders, as this topic is developing considerably. The issue of post-transplant lymphoproliferative disorder is of great interest to scientists and clinicians due to significant changes in its epidemiology, diagnostics and therapy over the last decade. The epidemiology of post-transplant lymphoproliferative disorders has been influenced by a tremendous increase in mismatched and unrelated donor transplants. Current diagnostics of EBV-associated diseases is based on modern pathology, quantitative viremia and the use of positron emission tomography. A significant progress has been achieved in the therapy of post-transplant lymphoproliferative disorders with the use of rituximab and EBV-specific cytotoxic T lymphocytes. This book seeks a more comprehensive application of the knowledge on EBV and its role in the development of cancer. The publication is not a purely academic monograph as it contains a number of novel insights, concepts and hypotheses. We are presenting a book related to both basic and clinical research, and whose main audience is the healthcare community.