Long neglected in scholarship, the so-called Grasnick 5 documents reveal Beethoven working out concepts and ideas, offering fascinating insights into his creative method. This critical edition, the third in the Beethoven Sketchbook Series, offers a facsimile and transcription of the contents of the stitched pocket sketchbook started by the fifty-year-old master during the summer of 1820. At the time, Beethoven labored over the Missa solemnis , Opus 123. The sketchbook's pages yield the entire record of his early ideas on the Agnus Dei of that work as well as a sketch for part of the Benedictus. Patrizia Metzler and Fred Stoltzfus decipher the quirks of the composer's workshopping--the infamous penmanship, multiple generations of pencil and ink marks, and omitted notation--and wrestle with the legibility issues inherent in the task of dealing with aged documents. Their commentary completes a fruitful scholarly journey and provides context for experts, musicians, and anyone else interested in this fraught period of Beethoven's creative life.