The Yarnall Library of Theology was established in 1911 at St. Clement's Episcopal Church, Philadelphia, for the use of the clergy and of all students of theology and ecclesiastical history. The collection was housed at the Philadelphia Divinity School from 1912 until 1974 when it was placed on deposit at the University of Pennsylvania Library. The collection consists of approximately 21,000 volumes shelved as a unit on the fourth floor of Van Pelt and approximately 700 rare books housed in Special Collections. The "stack" component circulates to all Penn library users. The collection supports specialized study in the fields of Anglican and Roman Catholic canon law, history, biography, liturgy and theology and in some related subjects.
The Yarnall Fund, still managed by St. Clement's Church, provides for the continued upkeep and enhancement of the collection; and the original collection development policy, as set forth by Ellis Horner Yarnall, was to "supply the deficiencies now existing in the collections accessible to the public in this department of literature in Philadelphia or even America [and] all books selected are to relate to the History, Doctrine or Worship of the Catholic Church, as treated by the early Fathers and Doctors, or those of the Mediaeval period, or recently by Anglicans."
Current collection development policy continues that set forth by Ellis Yarnall. Materials are acquired to complement the University's rich resources in patristics, canon law, medieval studies and 17th and 18th century British culture, and to extend the Library's holdings in Anglican and Roman Catholic liturgy and in English and Irish biography and local history. The Yarnall Library is developed in coordination with the bibliographer for Religious Studies, and every effort is made to minimize duplication with the University Library's own collection development.