This series comprises correspondence which is extensive, or significant, despite extent. Format includes: letters, cards, correspondence, print-outs of emails, copy correspondence and photocopies. Where responses by Rotblat are included, they are copies of outgoing letters, usually in Rotblat's hand (some are photocopies); or letters typed by a secretary. American spellings are retained, for example center. English summary translations included with Polish correspondence may have been done after the papers were received, and are not contemporary with the correspondence.