The glymphatic system (or glymphatic clearance pathway) is a functional waste clearance pathway for the mammalian central nervous system (CNS). The pathway consists of a para-arterial influx route for cerebrospinal fluid (CSF) to enter the brain parenchyma, coupled to a clearance mechanism for the removal of interstitial fluid (ISF) and extracellular solutes from the interstitial compartments of the brain and spinal cord. Exchange of solutes between the CSF and the ISF is driven by arterial pulsation and regulated during sleep by the expansion and contraction of brain extracellular space. Clearance of soluble proteins, waste products, and excess extracellular fluid is accomplished through convective bulk flow of the ISF, facilitated by astrocytic aquaporin 4 (AQP4) water channels.