This chapter examines Emil Kraepelin’s work in the field of ‘pharmaco-psychology’ that he performed as a trainee, his work in relation to therapeutics while conducting his pivotal clinical studies and the impact of his endeavours on the subsequent development of physical treatments in psychiatry. Evidence is accrued that Kraepelin was innovative in developing ways of examining the effects of drugs on psychological and behavioural function and it is argued that he is one of the founding fathers of what became the science of psychopharmacology. During his years of productive nosological research, Kraepelin was a relative sceptic about the positive effects of drugs on the outcome of mental illness and some of this was linked to his ideas about incurability and degeneration. He did examine the effects of some physical treatments, such as endocrine extracts and lithium, but was unimpressed by them and abandoned these approaches. The issue of whether his and his followers’ ideas regarding classification have helped or hindered research on physical treatments is discussed. While the use of categorical distinct mental illnesses is not supported by more recent research, nonetheless the pragmatic usefulness of Kraepelinian concepts has been associated with some therapeutic advances and benefits for patients. More complex methods of classification based on continua rather than categories are clearly needed and it is argued that Kraepelin would have approved of these approaches. What seems undoubted however, and represents his legacy that should be celebrated on the near centenary of his death, is his demonstration of the value of multi-disciplinary research and his advocacy of detailed clinical studies, including measures of outcome, which must remain the cornerstone of future therapeutic studies.