This book gives a concise review of the known human retroviruses; the onco-retroviruses HTLV-1 and -2 and the AIDS-associated lentiviruses HIV-1 and -2. History, classification, general and genomic structure, and basic biologic facts of retroviruses are described in introductory chapters. Subsequent chapters deal with the epidemiology, disease spectrum, structure and functions of the viral genes and proteins of the individual viruses. A separate chapter describes the various humoral and cellular immune mechanisms in response to HIV and their use with respect to diagnosis and treatment. Special attention is given to the complicated pathogenesis of AIDS and the consequences with regard to therapy and vaccination. The book ends with a critical review of recent work suggesting a possible role of still other retroviruses in human disorders including malignancies, autoimmune, or neurologic diseases. The book is designed to give the reader a broad, but detailed view of human retroviruses and the diseases associated with them. It tries to connect the viral, immunologic, and pathologic aspects of these infections to unifying concepts - no quick answers though, but profound critical information on a complicated topic.