 Birkenfeld was one of twenty German writers nominated to found a of PEN International, based on a resolution of the international organisation at its twentieth congress in Copenhagen.This followed consultation with PEN International's General Secreatary Hermon Ould, and with Wilhelm Unger representing the London exile group.The group of twenty fulfilled their mandate with a launch congress at Göttingen on 18–20 November 1948, under the leadership of Hermann Friedmann.