This article contributes to the knowledge of Jacob of Edessa's (d. 708) Old Testament revision by editing twenty texts (a total of 80 verses) from the Book of Isaiah and comparing them with the Greek recensions of the Septuagint, with the Peshitta, and the Syrohexapla. Two special features are introduced to set out Jacob's revision technique in some detail: 1. comparison with an earlier undeveloped stage of Jacob's revision extant in Ms Add 17,134 of the British Library; and 2. the distinction (by different colours and fonts) of the 'traditions' involved in the definite stage of his revision. Both features point to the emphasis given to the Peshitta in translating the substantial Greek text of the Old Testament.