In this preliminary chapter, we present a series of texts intended to clarify the way in which the summaries of doctrine and the doxographic manuals, to which we owe a large part of our information on the doctrines of the archaic philosophers, were produced during the course of the history of Greek philosophy and how some of them have been reconstructed by modern philologists. Although doxographical literature goes back to pre-Aristotelian sources, notably the sophist Hippias and Plato, the systematic investigation of the ‘opinions’ (doxai) of predecessors arises with Aristotle and Theophrastus, who are the ultimate source—beyond the compressions, transformations, and additions that accumulated in the course of time—of a handbook of which the most ancient version probably dates to the third century BC and which scholars customarily refer to as the manual of Aëtius. T17 illustrates how a version of that manual is hypothetically reconstructed on the basis of the various ancient authors who made use of it, T18 the way in which the summaries scattered throughout