The greatest need in clinical medicine today is for the long term control of cellular immunity. Coumarin, a simple molecule, and most of its derivatives, have been known for more than a century but their vital role in plant and animal biology has not been fully exploited. Coumarin prevents disease, modulates growth and maturation and defence systems and may have anti-oxidant properties. This volume presents a summary of the use of coumarins over a wide range of applications.