Morison's letters were generally dictated to his secretary and typed with a carbon copy. For the most part, it is these carbon copies that make up his outgoing correspondence in this series. (Where his original letters or photocopies of them are included, this fact is noted.) Letters to and from Morison are interfiled in one chronological sequence. Some short compositions by a particular correspondent are included in this series alongside that person's correspondence.

Letters and related items, mostly addressed to the editors of the Cambridge Review, and predominantly to Peter Hawkes. Some letters were intended for publication; most of the others concern the contribution (or otherwise) of articles and book reviews.