The first library at the North American College began 3 years after the founding of the college, when Rector Dr. McCloskey purchased three sets of the Minge’s Patrologia (copyright 1845) to form the foundation of the collection that is today housed in Randal Riede library. The Casa Santa Maria held the main library collection until 1953 when the new building on the Janiculum was opened and the seminary moved. The Randal Riede library is housed in the Pontifical North American College on the Janiculum. 

The main collection for the Randal Riede Library covers the areas of philosophy, theology, liturgy, scripture, canon law, spirituality and church history with particular emphasis on the church of the United States. Other areas include English literature and the area of science concerning bioethics. There are 64,000+ books and 234 periodical subscriptions. Approximately 1,000 new books are added to the collection each year. The strength of the library lies in the diversity of theological materials that span a century and in the number of books in the English language. The library houses the largest collection of books in English in the city of Rome. 

The Casa Santa Maria graduate library of the Pontifical North American College is housed in the building given by Pius IX to the American bishops in 1862. Though smaller, this library collection is rich in research collections of tomes and older books for doctoral students, especially in the area of Canon Law. The focus of this collection is on research in the various disciplines of theology, philosophy, and canon law with a preference for primary sources, critical reference materials, and periodical literature reflecting these areas of study. The Rare Book Room housed at the Casa Santa Maria is an outstanding feature of this library. 

Both libraries are completely cataloged according to the Library of Congress Catalog system. Each library has an online catalog available that contains all the holdings of the library. In house databases can be found in both libraries.