Hydrocephalus is an abnormal build-up of cerebrospinal fluid (CSF) in the brain. In normal circumstance, CSF is produced by the choroid plexus located in ventricles. CSF flows through the ventricular system to the cerebral and cerebellar subarachnoid spaces where it is reabsorbed into the blood circulatory system. Any obstruction of this pathway results in accumulation of CSF, which in turn compresses the surrounding brain tissue and causes the dilatation of CSF pathway spaces and the malfunction of central nerve system. Hydrocephalus may result from either impaired reabsorption or the production of CSF (communicating hydrocephalus) or blockage of CSF flow (non-communicating hydrocephalus). It can be caused by either congenital factors or acquired factors. Knowledge on the etiology and pathophysiology of hydrocephalus is important for the prevention and treatment of this disease. In this book, the prevalence of hydrocephalus is discussed, as well as risk factors and treatment options available.