This book presents the long-awaited critical edition of an unpublished manuscript of 277 pages containing Twardowski’s lecture notes on logic given in German at the University of Vienna. As to length, language and topic, this text is unique among the works of the author, who is renowned for his 'Zur Lehre vom Inhalt und Gegenstand der Vorstellungen' (1894), an influential but short book that has been out of stock for a long time already. In 'Logik' Twardowski’s ideas are exposed in a much more extensive and interestingly revised form. The rest of Twardowski’s production is in Polish, a language inaccessible to many readers.