 A text of Aëtius in a single column has now been published (Mansfeld and Runia 2020), superseding Diels’ text in two columns. The evidence of the primary and secondary sources for the reconstruction of each individual chapter is cited in full, though for Plutarch and Stobaeus only in the positive apparatus criticus. A detailed commentary follows. For each chapter its reconstruction from the witnesses is explained, its position in the context of the Placita and sometimes of the wider tradition determined, its contents and structure analyzed, such parallel evidence as is available, both earlier and later to much later, analyzed, and problems of interpretation raised by the text and contents of individual tenets are often separately discussed. Each chapter ends with a generous collection of further related texts to widen the horizon and place the topic of the chapter in the context of the history of ancient philosophy from beginning to end. These commentaries and collections of texts situate the Placita at a key point in the development over the centuries of Greek philosophy, looking backwards as well as forward. The existing remains amount to about six-sevenths of the original (see Jeremiah 2018).