In December of 1908, the Viennese physician Sigmund Freud received an intriguing invitation from the American psychologist G. Stanley Hall, inviting him to visit Clark University in Worcester, Massachusetts, and deliver a series of lectures describing his novel views about abnormal psychology. Freud delivered five lectures on five consecutive days from Tuesday, September 7 through Saturday the 11th. Given in German and following no written text, each was extemporaneously planned on a walk with Ferenczi earlier in the day. Freud's German version of the lectures has subsequently been re-translated into English, mainly to make all of their terminology consistent with the more recent "Standard Edition" of Freud's work. But the essence of all versions remains the same, and the original translation presented here has the historical virtue of enabling the reader to encounter Freud in exactly the same way his American audience first did in 1910.