Psychoneuroimmunology (PNI) is a field that has developed significantly during the last three decades; it has come to scientifically demonstrate the importance of the mind in the prevention, development and treatment of diseases. Throughout this chapter, we describe the evolution of PNI, the interaction of these systems to actively develop them, not only in adults but also in children. Similarly, it explains the influence of stress on the health of the individual and the importance of knowledge of psychoneuroimmunology to achieve the proper management of disease and quality of life. It also accounts for how psychological interventions have been proven effective and can serve as a model for researching and treating other diseases.