Since we are born, many dangerous microbes and malignant cells threaten our life. Therefore, we need to have powerful cells and molecules capable of defending us. We will call immune system to our body defenses, and immunocytes to the immune cells that protect us. Our immunocytes are very strong to attack threatening organisms and cells. However, they tolerate certain molecules such as self proteins, good microbes, food and harmless substances. Immunocytes communicate between them and with other cells through proteins called interleukins. In this book we will learn in a very simple and didactic way about our 38 interleukins and their role in health and disease.