 The relationship between logic and psychology was fought over most intensely in the German-speaking lands between 1890 and 1914. Indeed, during this period pretty much all of German-speaking philosophy was engulfed in the so-called Psychologismus-Streit (the ‘psychologism dispute’). This dispute centered on the question whether logic (and epistemology) are parts of psychology. Gottlob Frege and Edmund Husserl are the best-known figures of this controversy. The fact that the psychologism dispute has become closely associated with German-speaking philosophy must not, however, blind us to the enormous influence of John Stuart Mill upon both sides of the controversy. Paradoxically, Mill’s Logic of 1843 was not only a key inspiration behind much German-speaking psychologistic philosophy, it also contained some crucially important anti-psychologistic ideas.