The unexpected death of Adolf Johann Cord Rüter on August 11, 1965, has deeply affected his colleagues and co-workers, his students and his friends. But if for them all his decease was a grievous personal loss, for his country it was more; both the pursuit and the teaching of history have suffered inestimably through his passing. In the following pages an attempt will be made to give a brief outline of Rüter's work as a historian and a professor of history, an account of his activities as director of the International Institute of Social History in Amsterdam being left to a more competent hand.