The reader will find in this book alchemy in all its complexity, not as a mere product of fantasy but as what it certainly was: a science of Nature based on the metaphysical thinking of ancient humanism. This encyclopedia is not only proclaimed as the most extensive work of consultation, but is an attempt to restore alchemy to the place it deserves: between humanistic and natural sciences. With more than 200 entries, numerous illustrations and an exhaustive index, the reader will be able to form an idea of the characters, the materials, the symbols and the ideas that define what fundamentally is alchemy: a doctrine about the meaning and essence of the creation, and the place that man occupies in Nature and the Cosmos.