This chapter focuses on aspects of hydrocephalus that are common to all ages with a particular emphasis on the aging brain and the so called normal pressure hydrocephalus (NPH) syndrome, which is a chronic disease that likely evolved over a period of years. It has been clear for decades that the rate of ventricular dilatation and the state of brain maturation have a significant impact on the pathology, and possibly the pathogenesis of brain damage. Idiopathic NPH has been distinguished from chronic adult hydrocephalus associated with prior meningitis, brain trauma, or subarachnoid hemorrhage. The initial displacement may be at the expense of the subarachnoid compartment, the venous compartment, and the extracellular compartment with negligible damage to brain cells. Blood flow hypoperfusion leads to hypoxic-ischemic changes in the white matter, physical stretching compromises axon integrity, and retarded turnover of the cerebrospinal fluid (CSF) alters the extracellular microenvironment.