I shall be discussing Michael Polanyi's career as a scientist and philosopher from the point of view of history of science as well as his contribution to the history of science. But in order to arrive at my conclusions, I shall have to make some excursions into other fields, such as the branches of politics and epistemology that were fashionable during his career. For it is fair to say that Polanyi (1891–1976) was a unique person in the history of science, not least in the spectrum of his interests. The Dictionary of Scientific Biography (Vol. 18) lists his professional fields as chemistry, philosophy, and sociology.