This book arose from the combination of diverse areas of knowledge, experience, research, and points of view that try to demonstrate that mycobacteria are a complex science and very relevant to scientific studies that affect the human being in the world. Sophisticated techniques for improving human health do not guarantee that the "battle" against mycobacteria has been won, since tuberculosis, mycobacteriosis, and leprosy are a daily challenge in the world. The book includes contributions made by prestigious experts and research groups in different areas of mycobacteria, and they have contributed new perspectives of their area giving a comprehensive, important, and fascinating emphasis of this field that continues to offer challenges that lead various disciplines to understand their biology and pathogenicity. It is hoped that these chapters will be very useful for learning and discussion.