The correspondence is mostly incoming letters, telegrams, and postcards from individuals interested in submitting something to the Bulletin or requesting information about publications from M.H. Gill & Son; there are a few outgoing letters from the Bulletin editors or other Gill & Son employees. The correspondence dates from 1916 through 1987, the bulk of it from 1927-1933. Letters are written in a mixture of English, Irish, and some French; correspondents are located in the British Isles, United States, France, Italy, Germany, and elsewhere. Some letters are directed to John Joseph O'Kelly, not necessarily in his role as editor of the Bulletin and may be of a more personal nature.

There is also some financial documentation, both for the Bulletin and for O'Kelly's personal finances, and some documentation that appears related to preparing the Bulletin for publication. The correspondence has been arranged chronologically, with the financial and other documentation at the end of the series; correspondents' names have been noted when possible.