Composed by Théodore Dubois Twelve pieces is a set of Organ studies for upper intermediate players. Each piece is dedicated to a famous organist and an index at the beginning gives an English translation of the terms used in the book.

It features:
1. Prélude in F
2. Offertoire in E
3. Toccata in G
4. Verset de Procession in D
5. Offertoire in E flat
6. Verset-Choral in A minor
7. Fantaisie in E
8. Méditation in E flat
9. Marche des Rois Mages in E
10. Offertoire in E flat
11. Cantilène nuptial in A flat
12. Grand choeur in B flat

The most famous of these pieces is definitely the n3 Toccata in G which is also one of Dubois most renowned works. This piece also exists on its own as a separate score and can be found on the Musicroom website.