Although the German philosopher and psychologist William Stern (1871-1938) enjoyed wide renown in the early decades of the 20th century, very few contemporaries have any appreciable familiarity with his works. To the extent that his name is recognized at all, that is usually due to its historical connection with the concept of IQ, and this is all the more unfortunate because Stern's work in that particular domain was something from which he eventually sought to distance himself. On the other hand, Stern's greatest scholarly contribution, that comprehensive system of thought he called critical personalism, is one that could well be of great value to contemporary scholars. In particular, the distinction between persons and things, on which all of critical personalism rests, can serve to refine our understanding of the nature and limits of contemporary work in fields as diverse as personality studies and cognitive neuroscience. The present work is based on a series of public lectures given by the author when he was Ernst-Cassirer Guest Professor at the University of Hamburg in the summer semester of 2004. Its purpose is to provide contemporary readers with an introduction to William Stern that is both concise and accessible to lay persons and professionals alike.