Thomas Grubb’s recommended reading list:

First, Grubb’s own “My Time with Pierre Bernac

Bernac, P., The Interpretation of French Song, Gollancz/Norton (Paper Reprint)

Bernac, P., Poulenc, The Man and His Songs, Gollancz/Norton (Paper Reprint)

Grubb, T., Singing in French, A Manual of French Diction and French Vocal
Repertoire, Schirmer Books/Macmillan (Distributed by Cengage Learning)

Kimball, C., Song: A Guide to Art Song, Style and Literature,

Daykin, F., The Encyclopedia of French Art Song: Fauré, Debussy, Ravel,
Poulenc (Pendragon)

Noske, F., French Song from Berlioz to Duparc, Dover

Buckland, S. & Chimenes, M., Francis Poulenc: Music, Art, Literature, (Ashgate)

Poulenc, F., Correspondances, (ed. M. Chimenes, Fayard)

Poulenc, F., A batons rompus, Actes Sud

Poulenc, F., Journal de mes mélodies / Diary of My Songs, Gollancz

Daniels, K., Francis Poulenc, His Artistic Development and Musical Style, UMI
Research Press

Hell, H., Francis Poulenc, Fayard

Hahn, R., Du Chant / On Singers and Singing, Amadeus Press

Stricker, R., Les Mélodies de Henri Duparc, Actes Sud

Fauré, G., Correspondances, ed. J. Nectoux (Flammarion)

Bathori, J., Sur l’interpretation des Mélodies de Claude Debussy / The
Interpretation of the Songs of Claude Debussy, ed. L. Laurent (Pendragon Press)

Debussy, C., Monsieur Croche, Dilettante (a collection of critical writings by the
composer) (generally available)

Timbrell, C., French Pianism (Amadeus Press) and not just for pianists!

Johnson, Graham., A French Song Companion, (Oxford Press)