The sympathetic nervous system, as one of the divisions of the autonomic nervous system, significantly interferes with the regulatory mechanisms regulating the body's vital functions. Dysfunction of the sympathetic nervous system is associated with several health problems, including cardiovascular, digestive, renal, and other systems. It also plays a role in how the metabolism and dysfunction of the sympathetic nervous system affect the immune responses. Increased activity of the sympathetic nervous system also affects mental health, and it is a part of stress reactions, anxiety disorders, post-traumatic stress disorders (PTSD), and the like. In this book, we hope to cover the morphology and anatomy of the sympathetic nervous system and its arrangement, centers, afferents, efferents, and neurotransmitters as well as the experimental work linked to the cardiovascular, respiratory, renal, digestive, endocrine, and immune systems. We also hope to address the clinical problems associated with the dysfunction of the sympathetic nervous system at the various system diseases, but also connected to mental health and stress reactions.