This book is designed to provide the current state-of-the-field for CSF disorders that occur across the lifespan. The authors of the following chapters are true content experts and provide their accumulated knowledge, experience, and wisdom in addition to a thoughtful view forward. We begin with a discussion of the ventricles themselves, with changes in the ependyma that occurs throughout development and as the brain matures and then ages.  Pathophysiological changes and their role in hydrocephalus of various etiologies are considered.  Alterations in CSF composition, physiology, and flow are also discussed in the context of neurodevelopment and neurodegeneration.