The first critical edition of St. Ambroses Letters, CSEL 82/1 Epistularum libri I-VI, ed O. Faller (1968), 82/2 Epistularum libri VII-IX, ed. M. Zelzer (1990) and 82/3 Epistularum liber decimus, Epistulae extra collectionem, Gesta concilii Aquileiensis, ed. M. Zelzer (1982), is now completed by this volume containing a complete word index of the Letters and of the other documents edited in the third volume (the third Relatio Symmachi, the letter Optarem of pope Sirice and the Gesta concilii Aquileiensis) and the index of passages of the Bible and of source material. Added are an index of manuscripts and supplements including some remarks on the text of Fallers first volume. The complete word index will be of use for anybody interested in the characteristic features of the 4th century Latin.