A Book of Etudes is a collection of 45 studies. 18 of them are for solo marimba, 18 for solo vibraphone and 9 can either be played by vibraphone or marimba.
The studies are devided in 3 books:
Volume 1: 18 studies for solo marimba
Volume 2: 18 studies for solo vibraphon
Volume 3: 9 studies for solo marimba or solo vibraphon