Leprosy is a chronic granulomatous infectious disease that affects the skin and peripheral nerves; its causative agent is the obligate intracellular bacillus Mycobacterium leprae. The etiological diagnosis of the disease in its paucibacillary (PB) form still needs to be improved, because the bacillus is not yet cultivable. This book discusses the current challenges in the research of leprosy, as well as the epidemiology and treatment strategies available.