The correspondence of the Puritan divine Richard Baxter (1615-1691) is an unusually rich source of evidence for seventeenth-century history, in particular for the period's involved ecclesiastical history and its intellectual, cultural, and bibliographical tastes, as well as for Baxter himself. The 1250 or so extant letters, spanning 1638-1696 and varying in length from brief notes to mini-treatises, are exchanged with a very wide range of correspondents and touch on a great variety of topics, from pastoral advice and theological controversy to current political affairs and legislation. The great majority of the letters, often undated and unattributed, have never been published.

The present Calendar makes the substance of the correspondence fully available for the first time. The chronological sequence of the letters is established, correspondents are identified with full biographical information, and the occasional and essential subject of every letter is indicated. In the great majority of cases detailed summaries are given, often with extensive quotation verbatim; and all persons, books, and other matters of fact mentioned in the letters are glossed and annotated. There are also indexes of persons, of places, and of Baxter's works.

In the course of annotation and contextualization, the Calendar frequently corrects or expands standard reference works, while the letters themselves often supply previously unknown information about the period.