This chapter presents a comprehensive examination of the autonomic nervous system (ANS), focusing on its structural organization and functional significance in maintaining physiological homeostasis. The author synthesizes the current understanding of the ANS’s three major divisions—sympathetic, parasympathetic, and enteric systems—and their intricate interactions in regulating visceral functions. This chapter establishes the fundamental two-neuron arrangement that characterizes autonomic neural pathways, distinguishing them from somatic motor systems. The text details the precise anatomical organization of preganglionic neurons within the central nervous system (CNS) and their connections to postganglionic neurons in peripheral ganglia, emphasizing the structural basis for autonomic control. A significant portion of the work examines the central autonomic network (CAN), presented as a hierarchically organized system spanning multiple levels of the neuraxis. This network coordinates complex autonomic responses through integrated processing of visceral and somatic inputs. The analysis extends to a detailed examination of neurotransmitter systems, highlighting both classical transmitters and various neuropeptide co-transmitters that enable fine-tuned autonomic regulation. The author provides a detailed analysis of autonomic regulation in major organ systems, including cardiovascular, pupillary, pelvic, and gastrointestinal functions. The text particularly emphasizes the complex interplay between sympathetic and parasympathetic influences in maintaining physiological balance. Special attention is given to the enteric nervous system’s unique semiautonomous functioning within the gastrointestinal tract. This chapter concludes with an examination of thermoregulation and sweating, exemplifying the ANS’s role in maintaining homeostasis through multiple effector systems. Throughout the text, clinical implications are integrated with basic science, providing a comprehensive resource for both researchers and clinicians in understanding autonomic function and dysfunction. This comprehensive work represents a synthesis of classical understanding and contemporary research in autonomic neuroscience, offering a detailed yet accessible examination of this essential control system. This chapter serves as both an educational resource and a reference for further investigation in the field.