For All the Saints
- Article on the Nineteen Martyrs of Gorkum, including St. Nicholas Pieck. Omits gruesome details of how the martyrs were tortured, but does say that they refused to deny the Real Presence or the primacy of the pope.
- http://www.saintpatrickdc.org/ss/0709.htm#gork

Catholic Encyclopedia
- St. Nicholas Pieck, Franciscan, studied at Louvain, was ordained a priest. He was martyred in 1572. His name is sometimes spelled "Pick".
- http://www.newadvent.org/cathen/11065b.htm