As the designated archive of the Congregational Christian churches, the Library collects material on the history of the denomination from the Puritans to its present incarnation, holding all significant institutional records from the United Church of Christ, the National Association of Congregational Christian Churches, and the Conservative Congregational Christian Conference, before and after. The Library also holds some 1,500 different periodicals representing its longstanding interest in social reform, missionary work, and education. The Congregational Library also holds rare newspapers from the Christian Connection denomination.