Weber’s concept of “rationalization” is rightly seen as the core of his mature thought. At the same time, there has been increasing attention to his “ambivalence” towards the rationalization of economic, administrative and political process-es, and of the conduct of life altogether. The themes of his nationalism and the irrational tendencies of his complex personality have also become increasingly prominent. While nationalism may not be per se irrational, any nationalist is logically compelled (at least in principle) to recognize the legitimacy of other — possibly opposed — nationalisms. Weber attempted to avoid this paradox of nationalism by stressing the particular responsibility of larger states, albeit with the problematic concept of the “Herrenvolk.” This article explores Weber’s nationalism and current nationalist and populist tendencies, in the light of his conception of sovereignty, democracy and plebiscitary leadership (Führerdemo-kratie). “Sovereignty,” I suggest, has become a shibboleth in the twenty-first century, notably in the US, Russia, Tur-key, Hungary and Poland, and in the current debacle in the UK. Although Weber uses the word “sovereignty” very rarely, the concept is at the centre of his sociology of the state and also, I suggest, of his conception of rationalization. There is a parallel with his use of the term “nation.”