This PIR volume presents a comprehensive collection of reviews that focus on the role of the blood-brain barrier (BBB) during steady-state and inflamed conditions. Within the central nervous system (CNS) the constantly changing bloodstream is strictly separated from the CNS parenchyma by the BBB. However, viruses, bacteria, parasites and auto-aggressive immune cells can penetrate the barrier and significantly contribute to CNS inflammation. The BBB can actively contribute to neuroinflammation by presentation of chemokines, expression of cell adhesion molecules and alterations of barrier properties. As such, understanding the role of the BBB under healthy and pathological conditions is essential to the development of new drugs to efficiently combat inflammatory diseases of the CNS.