© 2013 Springer Science+Business Media New York. All rights reserved. The anatomy of the craniocervical junction is complex with an intricate intersection between lower cranial and upper cervical nerves and the osteology of the posterior fossa skull and the atlanto-axial joints. A comprehensive understanding of this morphology is important to those treating patients with hindbrain herniation. In this chapter, the surgical anatomy of the posterior fossa and its contents (cerebellum, brainstem, lower cranial nerves, vertebrobasilar arteries, cranial venous sinuses) and upper cervical spine and its related neurovascular structures are reviewed and in special regard to the anatomy encountered in posterior fossa decompression for the Chiari malformations.