Book excerpt: The chemistry of heterocycles is an important branch of organic chemistry. This is due to the fact that a large number of natural products, e. g. hormones, antibiotics, vitamins, etc. are composed of heterocyclic structures. Often, these compounds show beneficial properties and are therefore applied as pharmaceuticals to treat diseases or as insecticides, herbicides or fungicides in crop protection. This volume presents important pharmaceuticals. Each of the 20 chapters covers in a concise manner one class of heterocycles, clearly structuredas follows: * Structural formulas of most important examples (market products) * Short background of history or discovery * Typical syntheses of important examples * Mode of action * Characteristic biological activity * Structure-activity relationship * Additional chemistry information (e.g. further transformations, alternative syntheses, metabolic pathways, etc.) * References. A valuable one-stop reference source for researchers in academia and industry as well as for graduate students with career aspirations in the pharmaceutical chemistry.