1. Introduction: self-assertion and its alternatives in ancient scientific and technical writing Jason König; 2. Philosophical authority in the Imperial period Michael Trapp; 3. Philosophical authority in the Younger Seneca Harry Hine; 4. Iurisperiti: 'men skilled in law' Jill Harries; 5. Making and defending claims to authority in Vitruvius' De architectura Daniel Harris-McCoy; 6. Fragile expertise and the authority of the past: the 'Roman art of war' Marco Formisano; 7. Conflicting models of authority and expertise in Frontinus' Strategemata Alice König; 8. The authority of writing in Varro's De re rustica Aude Doody; 9. The limits of enquiry in Imperial Greek didactic poetry Emily Kneebone; 10. Expertise, 'character', and the 'authority effect' in the Early Roman History of Dionysius of Halicarnassus Nicolas Wiater; 11. The authority of Galen's witnesses Daryn Lehoux; 12. Anatomy and aporia in Galen's On the Construction of Fetuses Ralph M. Rosen; 13. Varro the Roman Cynic: the destruction of religious authority in the Antiquitates Rerum Divinarum Leah Kronenberg; 14. Signs, seers and senators: divinatory expertise in Cicero and Nigidius Figulus Katharina Volk; 15. The public face of expertise: utility, zeal, and collaboration in Ptolemy's Syntaxis Johannes Wietzke; 16. The authority of mathematical expertise and the question of ancient writing more geometrico Reviel Netz; 17. Authority and expertise: some cross-cultural comparisons G. E. R. Lloyd.