In the past, the blood-brain barrier (BBB) has been characterized mainly as a layer of endothelial cells forming the vessel/capillary wall of the brain. More recently, the BBB is considered to be a part of a highly dynamic and interactive system called the neurovascular unit (NVU), consisting of vascular cells, glial cells, and neurons.The list of central nervous system (CNS) pathologies involving BBB dysfunction is rapidly growing. The opening of the BBB and subsequent infiltration of serum components to the brain can lead to a host of processes resulting in progressive synaptic and neuronal dysfunction and loss. Such processes have been implicated in different diseases, including vascular dementias, stroke, Alzheimer´s disease (AD), Parkinson´s disease, multiple sclerosis, amyotrophic lateral sclerosis, hypoxia, ischemia, and diabetes mellitus. Tauopathies represent a heterogeneous group of around 20 different neurodegenerative diseases characterized by abnormal deposition of microtubule-associated protein tau in cells of the nervous system. Increased microvascular permeability has been more typically related to cerebrovascular deposition of amyloid-β (Aβ), but in contrast very little is known about the connection between functional impairment of the BBB and the misfolded tau proteins. Here, we review what is known about tauopathies, the BBB, and the NVU.