The library of the Centro Pro Unione is a specialized library in ecumenical studies, established at the end of 1969.

Since its foundation, the library maintains a close working relationship with other Roman libraries interested in interconfessional dialogue, especially with those of the Waldensian Faculty of Theology and the Anglican Centre.

The library has about 23,300 volumes and 400 periodicals. It offers scholars a large collection in ecumenical theology, history of the ecumenical movement and the World Council of Churches, history of Vatican II and substantial sections devoted to theology, liturgy, history and spirituality of Christian denominations, as well as an exhaustive documentation on interconfessional theological dialogues.

In addition, the library compiles a bibliography relating to interconfessional theological dialogues publisehd on the Semi-Annual Bulletin.

The bibliography currently has more than 32,500 records, updated daily and searchable in the online catalogue.

In 1991, the Centro joined the association URBE, a network of libraries of the major pontifical universities of Rome, and since 2003 it is a member of the American Theological Library Association.