The letters in this volume have been selected from Darwin's correspondence in the years between 1860 and 1870, that is, from just after the publication of Origin of species to just before the publication of Descent of man. At the time of writing, letters from 1860 to 1867 had been published in full in volumes 8 to 15 of the Correspondence of Charles Darwin (CUP, 1993–2005). As with the first volume of selected letters (Charles Darwin's letters: a selection 1825–59, CUP 1996, revised edition 2008), the editors have sought to make the selection representative of the larger work and to provide a trustworthy portrayal of Darwin's mind, personality, and method of work. This volume of selected letters includes letters to Darwin as well as letters from him, enabling readers to follow the developing dialogues between Darwin, his friends, family, and readers.

The texts of the selected letters for the most part retain the spelling and punctuation of the originals. Editorial interpolations and corrections, made only where the text would otherwise be hard to understand, are placed in square brackets, and all editorial omissions are indicated by ellipses. Where Darwin used Down headed notepaper to write from another address, his true location has been added to the address in square brackets. Square brackets have also been used to disambiguate addresses, for example ‘Cambridge [Massachusetts]’.