Most of the letters, 1897-1926, relate to academic and research matters, many of them bibliographical queries, or to J. H. Davies's researches and publications. Some concern professional matters and developments at the Cardiff Free Libraries and later the National Library of Wales where Ballinger was the first chief librarian. Some of the later letters relate to the establishment and early growth of the National Library and to Davies's membership of its court, council and internal committees. There are many references to the National Library's campaign to secure the status of a copyright receipt (legal deposit) library and to wrest improved funding from the exchequer, and some to the deposit of the early archival collections and printed works at the Library. There are a few references to family life. A few of the letters from the Cardiff period are written by Harry Farr on behalf of Sir John Ballinger.

The letters, 1895-1925, discuss Welsh political life, the attempts to regenerate Mudiad Cymru Fydd, historical records relating to Flintshire, the foundation of the National Library of Wales, its location at Aberystwyth, and appeals for increased government funding and the passage of the copyright legislation, developments at the University College of Wales, Aberystwyth, and the federal University of Wales, the possibility of establishing a Public Record Office for Wales, and the selection of Liberal candidates in Welsh constituencies for the 'Coupon' General Election of December 1918.