Stress refers to the process of adaptation of an individual once he/she is exposed to external or internal challenges. The organism possesses numerous systems to coordinate such adaptive responses, both at the systemic and the cellular level. In this book, we address stress-related bodily disorders, and, consequently, the mechanisms that participate in the crosstalk between the brain and the body; mainly the endocrine, the immune, and the autonomic nervous systems. Maladaptation may result in stress-related disorders, which eventually affect all organ systems and can involve central and peripheral mechanisms since this crosstalk is truly bi-directional.