Frederick Burkhardt (1912-2007), the founder of the Darwin Correspondence Project, was president of Bennington College, Vermont, 1947-57, and president of the American Council of Learned Societies, 1957-74. Before founding the Darwin Correspondence Project in 1974, he was already at work on an edition of the papers of the philosopher William James. He received the Modern Language Association of America's first Morton N. Cohen Award for a Distinguished Edition of Letters in 1991, the Founder's Medal of the Society for the History of Natural History in 1997, the Thomas Jefferson Gold Medal of the American Philosophical Society in 2003 and a special citation for outstanding service to the history of science from the History of Science Society in 2005. James A. Secord has served as Director of the Darwin Correspondence Project since 2006. He is also Professor of History and Philosophy of Science at the University of Cambridge and a fellow of Christ's College. Besides his work for the Darwin Project, his research focuses on the history of science from the late eighteenth to the early twentieth centuries. His book, Victorian Sensation: The Extraordinary Publication, Reception, and Secret Authorship of Vestiges of the Natural History of Creation (2000), won the Pfizer Prize of the History of Science Society. He has recently written on scientific conversation, scrapbook-keeping and public scientific displays.

'The consistently high-quality edition of the complete correspondence, to and from, Charles Darwin has now reached its twenty first volume and the year 1873. … As always with these volumes, there is so much to find and so much to increase our understanding of this truly great scientist.' Michael Ruse, The Quarterly Review of Biology

• List of illustrations; List of letters; Introduction; Acknowledgments; List of provenances; Note on editorial policy; Darwin/Wedgwood genealogy; Abbreviations and symbols; The Correspondence; Appendix I. Translations; Appendix II. Chronology; Appendix III. Diplomas presented to Charles Darwin; Appendix IV. Reviews of Expression; Appendix V. Draft subscription list for Thomas Henry Huxley; Manuscript alterations and comments; Biographical register and index to correspondents; Bibliography; Notes on manuscript sources; Index.