Canine leishmaniosis is one of the major zoonoses that cause severe fatal disease in humans and dogs globally. Infections caused by different Leishmania species are present in a variety of regions with different climatic conditions in the Old and New Worlds. This chapter looks at Leishmania species that infect dogs and their geographical distribution; life cycle and transmission of L. infantum in dogs; pathogenesis, clinical presentation and clinicopathological findings; diagnosis; therapy, prevention and public health considerations; feline leishmaniosis.