 The twelve new editions of Berlin’s works published by Princeton University Press in 2013, 2014 and 2019 all contain significant additional material and new forewords by experts in the relevant fields, as does the Brookings Classics edition of The Soviet Mind (2016). A new foreword by Andrew Marr was added in the second edition (Vintage, 2014) of The Proper Study of Mankind. Page references in this article are to the latest editions of Berlin’s books, though the date of the first edition is used to identify them. Concordances that enable readers to find corresponding pages in earlier editions are available  online.