This book provides the first edition of all testimonia on the Sceptic philosopher Aenesidemus of Cnossus, deemed to be the source of Sextus Empiricus, the main representative for us of ancient Scepticism. It will be an essential reference work for all those scholars and students dealing with the history of ancient Scepticism. It provides an extensive philosophical and historical commentary, and throws light on a series of questions concerning the philosophy of the late Academy, Stoic Heracliteanism, and the interaction between medicine and philosophy in the late Hellenistic era.