Paracelsus was one of the most important figures in the intellectual history of the first half of the sixteenth century. He is as famous today as an alchemist as he is for being a pioneering physician. The document examined here, Concerning the Nature of Things, which he probably wrote in 1537 (but which was not published until 1572), gives an overview of his thought, which influenced the development of modern science as well as homeopathic medicine and various forms of occultism. It begins with a detailed exposition of perhaps Paracelsus's most bizarre and evocative idea, the creation of an artificial human being, or homunculus.