The choroid plexus is a fascinating specialization of the ependymal lining inside the cerebroventricular system of the human brain. The choroid plexus receives blood vessels that branches into wide diameter fenestrated capillaries that sustain tissue function. A cuboidal epithelial monolayer resides over the core of sparse connective tissue and represents the principal component of the blood–cerebrospinal fluid barrier. The choroid plexus epithelium is the main source of cerebrospinal fluid. The cells secrete simple ions and water through a complex expression of specialized plasma membrane proteins such as pumps, channels and carriers in ordered and polarized fashion. In this chapter, we describe the gross and microscopic anatomical features of the choroid plexus, the molecular identity and significance of the membrane proteins of relevance to cell adhesion, barrier function and cerebrospinal fluid production.