Although tension-type headache is the most frequent primary headache, little is known about its pathophysiology. It is a matter of debate if the pain in tension-type headache originates from myofascial tissues or from central mechanisms in the brain. This article presents a summary of available data on the pathophysiology of tension-type headache and proposes a pathogenic model. From experimental research and clinical studies, it appears that myofascial nociception is important in episodic tension-type headache; however, central mechanisms (ie, central sensitization) are preponderant in the pathophysiology of the chronic form. Understanding the mechanisms of this central sensitization could allow for more efficient prophylactic treatments to emerge.