Emil Kraepelin, the creator of clinical–empirical psychiatry, is regarded today as one of the most important figures in the history of psychiatry. Wilhelm Wundt, the founder of scientific psychophysiological experimental psychology, had significant influence on both Kraepelin’s personal and scientific formation. Having met Wundt and attracted his attention when studying at Leipzig University in 1877, Kraepelin later approached him for personal advice when dissatisfied with his job as registrar at the Munich asylum under Gudden. After coming to Leipzig, Kraepelin worked at Wundt’s laboratory in 1882/1883, hoping that applying experimental psychological methodology to mentally ill patients would give him a better understanding of the various mental illnesses, which had largely not yet been differentiated from each other. However, in the following years Kraepelin’s efforts to reach his original research objectives were not crowned by any lasting success, but instead led to the formation of a pluridimensional concept. In contrast to the pre-eminent position experimental psychology had had for him earlier, during the 1890s he merely grouped it as one of several auxiliary sciences to psychiatry. In this chapter we review this consequential change in Kraepelin’s viewpoint based on personal correspondence from Kraepelin to Wundt.