- Encyclopedia Britannica: Gregorian Reform
- Oxford Bibliographies: Gregory VII
- Encyclopedia Britannica: Roman Catholicism
- Blog, Medieval Church History: Lesson 18: The Gregorian Reform & the Investiture Struggle
- Historyisfun: Gregorian Reform Movement
Books and Articles:
Lambert, Malcolm. Medieval Heresy: Popular Movements from Gregorian Reform to the Reformation. Barnes and Noble, 2nd edition, 1998.
Ozment, Steven. The Age of Reform, 1250-1550: An Intellectual and Religious History of Late Medieval Europe and Reformation Europe. Yale University Press, 1981 Edition.