Langue musicale universelle (book)
The second major book about Solresol, written by the other major contributor to Solresol, Boleslas Gajewski.
While originally written in French, translations can be found online in English, Spanish, German, Portuguese, and Russian.
(French) THE original book about Solresol, written by creator François Sudre.
(French) THE original book about Solresol, written by creator François Sudre, with some pages correctly re-arranged, and converted to DjVu format.