Cats, with a global population estimated at 600 million, are considered the most popular pets worldwide, and are adapted to all the environments and to different lifestyles. We can distinguish different types of cat populations, according to their living, which raise different concerns on respect to neutering or contraception. Feline Leukemia Virus (FeLV) was the first retrovirus isolated in domestic cats, and the infection is associated with a wide variety of clinical syndromes, including feline acquired immunodeficiency syndrome (AIDS or fAIDS). Inflammatory diseases of the oral cavity are common feline medical conditions and are associated with infectious agents such as Feline Immunodeficiency Virus (FIV), FeLV, herpesvirus (FHV-1) and calicivirus (FCV). The most common oral diseases in cats are gingivostomatitis, periodontal disease, tooth resorption and chronic periapical lesion by the canine tooth fracture. This book discusses the common diseases, clinical outcomes and developments in the veterinary healthcare of felines.