The vagus nerve performs many different functions in the human body. Understanding these functions helps inform the potential side effects of vagus nerve stimulation (VNS). The nerve consists of 80% afferent fibres [1,2]. These include visceral sensory and taste fibres which travel primarily to the nucleus of the tractus solitarius, as well as cutaneous sensation fibres from the external auditory meatus which project to the spinal nucleus of the trigeminal nerve. The efferent component includes branchial motor fibres from the nucleus ambiguus, parasympathetic fibres primarily from the dorsal nucleus of the vagus and parasympathetic fibres from the nucleus ambiguus to the heart. The motor fibres innervate skeletal muscles in the head and neck involved in speech production and swallowing, while the parasympathetic fibres innervate most of the viscera serving to control heart rate, respiration, gastrointestinal motility and many other autonomic functions. The majority of fibres in the vagus nerve consist of unmyelinated C fibres, but commensurate with its wide variety of functions, it also contains larger and faster-conducting A- and B-type fibres. The brainstem nuclei that receive vagal inputs integrate homeostatic information, provide commensurate adjustments to autonomic functions and also send this information to other brainstem nuclei projecting widely throughout the brain.