The opinion of W. H. S. Jones that Oribasius is 'an author that nobody wishes to read through' is probably coincident with the view of most Classicists who have ever read the Medical Compilations to judge from the almost total neglect Oribasius has suffered. Translations of the whole work have appeared only in Latin and French. This thesis is an attempt to redress this injustice, and the commentary is designed to indicate Oribasius' source for each quotation or paraphrase, assess the accuracy and comprehensibility of the contents, and discover the reasons behind the recommendations and rejections of certain cakes, breads, fruits, and vegetables, the emphasis being on ancient food and diet rather than medicine and philosophy. Books 1 and 4 are linked by their common themes of grains and breads, and thus have been chosen for examination. With the absence of any modern work on ancient Greek cuisine, and with the fullest accounts of Roman cooking often lacking in detail or accuracy, particular care has been taken to supply as full a set of references as possible which will perhaps prove useful for further study. The text on which the commentary is based is that prepared with great thoroughness and accuracy in 1928 by J. Raeder with some small changes. The translation, the first into English, offers no claims at elegance, but is there merely to assist with the reading of the Greek text. The thesis ends with both an index listing according to the forms in which they appear all the words in Books 1 and 4, with the exception of some common particles, and also a general index.