The International Headache Society (IHS) is the world's leading membership organisation for those with a professional commitment to helping people affected by headache.

As a charity, the purpose of IHS is to advance headache science, education, and management, and promote headache awareness worldwide.

Society's international journal is Cephalalgia.

International Headache Society Classification

Posttraumatic headache (PTH) is defined by the International Headache Society as: “a headache developing within seven days of the injury or after regaining consciousness”