The late E.P. Thompson described himself as ‘a historian in the Marxist tradition’ But when he embraced the Rule of Law (in Whigs and Hunters, many of his colleagues on the left ostracized him as an apostate. This essay argues that Thompson's critics have largely misunderstood what he meant by the Rule of Law. His was a minimal and historical conception, which merely sought to distinguish states whose rulers had unfettered discretion from states whose rulers were constrained by legal rules, whatever their source and contents. Also, in contrast to other radical theorists, Thompson recognized that law would be a necessary institution in any complex society, no matter what its economic basis, to mediate social relations. The essay concludes with some thoughts about the relevancy of Thompson's conception of the Rule of Law for ongoing efforts to revitalize a more `radical liberalism'.