Headache is a vast field with many different varieties of headaches and classifications. However, all headaches have a common anatomy and physiology. All headaches are mediated by the trigeminocervical nucleus, and are initiated by noxious stimulation of the endings of the nerves that synapse on this nucleus, by irritation of the nerves themselves, or by disinhibition of the nucleus. A mastery of the relevant anatomy and physiology of the trigeminocervical nociceptive system serves to predict and summarise the many varieties of headache systematically and with reference to their mechanisms.