This chapter will address the receptive mechanisms of vomiting initiated by noxious substances or forces acting through the digestive tract and the chemoreceptor trigger zone (CTZ). Some may consider motion sickness a noxious form of emesis, but this subject will not be addressed here. Emesis caused by noxious substances serves a protective function and involves receptors located at different levels within the neuraxis. Pre-absorptive noxious receptors are located in the mucosa of the digestive tract [1] and the post-absorptive noxious receptors are located in the CTZ of the brain [2]. Clinically relevant agents or forces, eg radiation [3] or cytotoxic drugs [4], may cause emesis by activating receptive mechanisms for noxious stimulationinduced vomiting. Before describing the receptive mechanisms of noxious stimulation-induced emesis, a brief description of the motor events of emesis will be provided in order to better understand functions of the emetic response.