The Darwin Correspondence Project is researching Charles Darwin's letters and has so far located more than 15,000 he either sent or received. The full texts of these are being published in The Correspondence of Charles Darwin (20 vols to date, CUP 1985-), and are also going online on the Project's website with 7500 currently available to read for free (www.darwinproject.ac.uk). Around half the original letters are in the Darwin archive in Cambridge University Library where the Project is based, with the rest spread in archives and private collections around the world; more are discovered every year. The research presented here was carried out as part of the "Darwin & Gender" project.