The first successful isolation of cerebral microvessels from rat brain some 30 years ago opened the way to the development of in vitro models of the blood-brain barrier (BBB), which have since contributed considerably to the understanding of the physiology, pharmacology, and pathophysiology of the BBB (1 ). However, the ever increasing number of in vitro models and techniques also creates problems that make transferability of results obtained with different models difficult even for experts, while scientists new to the field often find it hard to choose an optimal model for their particular interests. This chapter gives a brief overview of the current status of in vitro BBB models currently used and provides some guidance through the host of models with regard to their suitability for specific applications.