The autonomic nervous system (ANS), formerly known as the vegetative nervous system, is a division of the nervous system that supplies smooth muscle and glands, and as a result influences the function of internal organs. Called the ANS for its unconscious regulation bodily functions it is critical in delivering fuel and nutrients throughout the nervous system. This module discusses the central and peripheral components that make up the ANS and how breakdown in these systems lead to the development of various dysautonomia. Diagnostic, examination, and treatment applications will be explored when appropriate.