In 1948 Karl Popper sent a copy of his paper, 'Utopia and Violence', to Michael Oakeshott. Popper had recently read Oakeshott's essay 'Rationalism in Politics', appreciating its relevance to views he had expressed in The Open Society. Oakeshott wrote to Popper at some length, explaining his thoughts about reason, tradition and kindred matters, to which Popper responded. This paper reproduces these letters and discusses them with reference to pertinent writings of Popper and Oakeshott. While showing there was much common ground between the two men and that they significantly influenced each other, the writings reveal important differences over the role of reason and tradition in social and political life.