Charles Darwin's correspondence is a prime source for understanding the intellectual revolution in which he was a central figure. As well as revealing how Darwin went about his work, the letters bring out the doubts and anxieties, the false starts and disappointments, which do not feature in his publications. This Calendar is a catalogue of the letters the editors of the Correspondence of Charles Darwin have found to date. Information on the source and location of each letter is given, together with a brief summary of the content. First published in 1985, it has been amended to take account of recently discovered material and re-interpretations or re-dating of known letters. A new supplement section includes over 1500 amendments to the main body of the text together with over 500 newly found addenda.