The cat has been living in close association with humans for at least 3500 years, the ancient Egyptians routinely used cats to keep mice and other rodents away from their grain. The history of domestic cat may stretch back even further, as 8,000 year-old bone of humans and cats were found buried together on the island of Cyprus. Cats are social, extroverted cats that love human companionship and like being part of whatever's going on. They often attach strongly to one person, demanding constant attention from that person. Currently, the cat is the world's most popular household pet. The domestic cat is the definitive host for Feline leukemia virus (FeLV) and the virus has a worldwide distribution. FeLV is a retroviruses that represent one of the most common and important infectious diseases of cats worldwide. It is responsible for more death among cats than any other infectious disease. This book illustrates the introduction, rapid diagnosis, prevalence, treatment, prevention and control of FeLV in cats.