The fragmentary text known as the eighth book of the Stromata has puzzled Clementine scholars for centuries. For the most part, it consists of purely philosophical material concerned with the theory of demonstration and the method of scientific inquiry. But it also includes elements unmistakably Christian. Since the 17th century several theories have been proposed about its origin and purpose. This paper will offer a critical overview of these theories, with a special focus on the Nautin hypothesis published in 1976. The results of the most recent inquiry, viewing the text as a collection of excerpts from a lost writing of Galen, will be presented as well.