BN Cat. gén. 1960-1969 : Holtrop, Johan Willem
BN Cat. gén. : Holtrop, Jan Willem
Biogr. arch. Benelux
Catalogus librorum saeculo XV impressorum, quotquot in bibliotheca regia hagana asservantur
/ edidit Joh. Guill. Holtrop, 1856
Grove Winkler Prins, 9de druck
Henry Bradshaw's Correspondance on incunabula with Johan Willem Holtrop and Marinus
Frederick Andries Gerardus Campbell / ed. by Wytze and Lotte Hellinga, 1966
Internet, http://webopc.konbib.nl (Bibliothèque royale, Pays-Bas), 2000-05-16 : Holtrop,
J. W (Johannes Willem)
LCNA (CD), 1996-06 : Holtrop, J. W. (Jan Willem)