Interpretability in Terms of Models1)1)This paper, which reports a talk given before the Euratom workgroup in Amsterdam in the fall of 1962, was prepared partly at the University of Amsterdam under Euratom Contract No. 010–60–12 and partly under United States National Science Foundation Grant No. NSF–GP 1603 (Montague). I am grateful also to Dr. K. L. de Bouvere and Professors Andrzej Ehrenfeucht, Solomon Feferman, and Alfred Tarski for helpful discussion; Professor Tarski made suggestions leading to the improvement of several formulations.