Book excerpt: 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, the Calendar has been amended to take account of recently-discovered material and re-interpretations or re-dating of known letters. A new supplement lists over 1000 amendments to the main body of the text, together with over 500 addenda relating to newly- discovered material.