Leishmania parasites are a group of pathogens responsible for diseases known as leishmaniases. These pathologies affect predominantly the poorest people, mainly in tropical countries, exerting a high impact on mortality and morbidity rates. The absence of a vaccine and the reduced drug arsenal, associated with the diversity in the clinical presentation and hosts, highlight the complexity of the disease and its position as a worldwide public health problem. This book addresses different aspects related to leishmaniases, such as epidemiology, immunopathology, and the challenges of disease in humans and domestic animals. The information presented contributes to a better understanding of the Leishmania parasites and different clinical forms produced by infection, as well as their distribution around the world and their impacts on public health.