On the development of interpolation - instead of a history three letters

This compilation should be viewed as a kind of prolegomena to a history of interpolation. Three letters from Mischa Cotlar, Antoni Zygmund and Olof Thorin from c. 1980 are reproduced. Thorin's letter is given in translation. These letters were written as a reply to an inquiry by the editor/translator. It is remarkable that while Thorin spent his whole professional life as an actuary, neither of his two publications in interpolation were covered by Mathematical Reviews nor by the Zentralblatt fur Mathematik. On the other hand, Cotlar, in his letter, gives a disclaimer to a rumor that he had rediscovered Marcinkiewicz's interpolation theorem while studying under Zygmund in Chicago in the mid 1950s. The editor/translator makes an Appeal to all Readers who might have further information about the founding years of the theory of interpolation spaces, i.c. the years just before or after 1960, to send him similar letters.