This book provides, using examples of fluorinated drugs, a critical approach to the influence of fluorine on a molecule´s biological behaviour and structural properties of a molecule. The first part introduces the preparation of fluorinated compounds and their specific properties. The second part deals with fluorinated analogues of natural products, fluorinated amino acids and peptides, and derivatives of sugars. This section also includes a detailed chapter about the conception of enzyme inhibitors. In the final part, the main fluorinated pharmaceuticals, marketed or in development, are classified according to their therapeutic classes.