A new reconstruction and text of the Placita of Aëtius (ca. 50 CE), accompanied by a full commentary and an extensive collection of related texts. This compendium, arguably the most important doxographical text to survive from antiquity, is known through the intensive use made of it by authors in later antiquity and beyond. Covering the entire field of natural philosophy, it has long been mined as a source of information about ancient philosophers and their views. It now receives a thorough analysis as a remarkable work in its own right. This is the five-volume set of studies on Aëtius (1996–2020): Aëtiana I (ISBN: 9789004105805, 1996), II (Parts 1 ISBN 9789004173569 and 9789004169876; 2008), III (ISBN 9789004180413; 2009), IV (ISBN: 9789004361454, 2018), and V (Parts 1-4; ISBN 9789004428348, 9789004428355, 9789004428362, 9789004428379; 2020). It uses an innovative methodology to replace the seminal edition of Hermann Diels (1879).