This edition presents Rée's books Psychologische Beobachtungen (Psychological Observations) (1875), Der Ursprung der moralischen Empfindungen (The Origin of Moral Sensations) (1877), Die Entstehung des Gewissens (The Genesis of Conscience) (1885) and Die Illusion der Willensfreiheit (The Illusion of Free Will) (1885). Together with a sketch of Rée's biography and the history of his works, which makes hitherto unknown documents accessible, Treiber reveals numerous sources for Rée's texts. In addition, he reproduces available contemporary reactions to the publications.