The cephalic phase of nutrition refers to a set of food intake-associated autonomic and endocrine responses to the stimulation of sensory systems mainly located in the oropharyngeal cavity. These reactions largely occur in the digestive system, but they have also been observed in other structures. Most published data indicate that cephalic responses are mediated by the efferent component of the vagus nerve, although other neurobiological components and brain centers must be involved. The physiological significance of all of these reactions has yet to be fully elucidated, but when the cephalic phase of digestion is obviated major physiological and behavioral dysfunctions can be observed. This has led numerous authors to propose that their function may be essentially adaptive, preparing the digestive system for the reception, digestion, and absorption of the food. Study of the neural/cephalic phase and the consequences of its absence may have clinical relevance in the setting of artificial nutrition, and may explain the difficulties of providing enteral nutrition to many of the patients that require it.