This chapter provides the reader with a succinct review of the current literature regarding bovine lymphoma. Historically important events are mentioned, but the reader must rely on the cited sources for comprehensive background information. Lymphoma is the second most common malignancy in cattle, but it is the most frequent hemolymphatic neoplasm. Semipurified membrane preparations from bovine lymphoid tumors caused delayed cutaneous hypersensitivity reactions in six cattle with lymphoma, while three controls failed to react. Infection with bovine leukemia virus (BLV) is widespread in domestic cattle. Fortunately, the only disease associated with BLV infection is lymphoma and this is a relatively rare event. The protection of export markets gives economic justification for the development of vaccines and control programs. As a result of the remarkable advances in the molecular biological aspects of BLV, it is likely that the one gene in the bovine genome will soon be identified.