Fluorine is the most reactive of the elements and its incorporation in a molecule more often than not imparts interesting, if not dramatic, changes of properties. As such, fluorine-containing materials have important commercial applications in pharmaceuticals, agrochemicals, plastics and polymers, surface modification, electronics, solvents, and as refrigerants. Indeed life would be much more difficult if it were not for fluorine! From an academic point of view, fluorine has opened up a whole new branch of "unnatural" chemistry, rich in unexpected and novel reactions, and has proved to be an invaluable mechanistic probe.