A first-time collection of cutting-edge morphologic, permeability, transport, in vitro, and molecular techniques to study the workings of the blood brain barrier in health and disease. Described in step-by-step detail, each readily reproducible method includes an explanation of the theoretical basis of the method, a discussion of its advantages and limitations, notes on avoiding pitfalls, and examples of results obtained using the technqiue. These powerful tools can be used to isolate undiscovered molecules, deepen our understanding of their role in health and disease, and identify targets for future gene therapy and therapeutic intervention.