The Benedictine Abbey of Lambach in Upper Austria boasts a long and distinguished history as a center of musical life in Central Europe. The monastery's music tradition flourished most actively and significantly in the 18th century, but especially during the reign (1746 to 1794)of Abbot Amandus Schickmayr. Schickmayr, described by one contemporary as excessivus amator musicae, was an astute patron who maintained close personal ties with leading musicians of the day - in particular, the Mozarts, father and son, and Michael Haydn - as well as an avid collector who no doubt encouraged the acquisition of the greater number of works among the holdings of the abbey's music archive today. The collection at Lambach became in time, and remains to the present day, one of the most extensive repositories of music manuscripts at any of the Austrian monasteries. Its holdings are understandably rich in sacred, theatrical and symphonic works by Michael Haydn, the two Mozarts and others in the Salzburg Kapelle. Equally important, however, are its manuscripts of early symphonies by Joseph Haydn and ofworks in various instrumental genres by Carl Ditters von Dittersdorf; Carlos d'Ordonez; AntonNeumann; Georg Christoph Wagenseil; and Johann Baptist Wanhal. In 1768, abbey organist Anton Obermayr compied a351-page inventory of the music manuscripts on hand at Lambach in that year. The importance of Obermayr's catalog rests in its provision of terminus post quem dating for more than 1300 works which are cited, not only with bass incipit and particulars of scoring, but in nearly all cases also with composers' names. Our edition presents the Lambach thematic catalog in facsimile with annotations identifying its entries with melody incipits where possible and indicating: (1) whether the corresponding music manuscript is extant or missing; and (2) if extant, describing the source in full - its present-day shelf number, whether compete or incomplete, paper and water-marks, and identification of copyists by name or by internally coherent system (e.g., Copyist 39). An appendix provides similar bibliographical citations for more than 1000 additional manuscripts in the music archive at Lambach but which came to the collection after the thematic catalog had been drawn up.