Beethoven’s Grosse Fuge, published in 1827, appears to be the first work to have been allocated rehearsal letters, which were added before publication. The rehearsal letters can be compared with the work’s structure, which is best perceived as dividing into three main ‘movements’, the third being much the longest. A different approach is necessary for analysing each of the three. In the first, reference to medieval rhythmic modes helps to clarify Beethoven’s procedure. The second is essentially a fugue, albeit unusually homophonic. The third is multi-partite and includes two fugal expositions. Thus there are four full fugal expositions altogether; each is a double fugue in which the exposition is more or less regular. The rehearsal letters match up well but not perfectly with the structure of the work.