Designing a comprehensive and practical classification schema for headache disorders has been an elusive goal for many reasons. The International Classification of Headache Disorders, 2nd Edition (ICHD-II) is the best attempt to date, but it, like its predecessor the ICHD-I, is plagued with a number of limitations. It was designed as both a research and clinical tool but can be frustrating for practitioners in either area. Primary headaches, such as migraine, chronic daily headache, and "other" headaches, such as new daily persistent headache, are particularly problematic sections of the classification. In addition, classification of a number of more complex (ie, where pathophysiology is poorly understood) secondary headaches, such as medication overuse and posttraumatic headaches, is also vexing. This chapter is an attempt to summarize the ICHD-II, focusing on primary headache types, and suggest best practices for usage of it.