The International Classification of Headache Disorders, 3rd edition (beta version) is freely reproducible for scientific, educational, or clinical use by institutions, societies, or individuals. Commercial reproduction requires permission from the International Headache Society. The document is available in English and translations are permitted for field testing and education, but must be registered with the society. The classification is hierarchical, allowing for detailed diagnoses ranging from first to fifth digit levels. It covers primary and secondary headaches, with detailed criteria for each type. The primary headaches include migraine, tension-type headache, trigeminal autonomic cephalalgias, and other primary headache disorders. The secondary headaches are attributed to various conditions such as trauma, vascular disorders, non-vascular intracranial disorders, substances, infections, and psychiatric disorders. The classification aims to improve diagnostic accuracy and guide research and clinical practice.The International Classification of Headache Disorders, 3rd edition (beta version) is freely reproducible for scientific, educational, or clinical use by institutions, societies, or individuals. Commercial reproduction requires permission from the International Headache Society. The document is available in English and translations are permitted for field testing and education, but must be registered with the society. The classification is hierarchical, allowing for detailed diagnoses ranging from first to fifth digit levels. It covers primary and secondary headaches, with detailed criteria for each type. The primary headaches include migraine, tension-type headache, trigeminal autonomic cephalalgias, and other primary headache disorders. The secondary headaches are attributed to various conditions such as trauma, vascular disorders, non-vascular intracranial disorders, substances, infections, and psychiatric disorders. The classification aims to improve diagnostic accuracy and guide research and clinical practice.