The library and documents owned by Guido Adler (1855-1941), who was one of the most prominent representatives of musicology of Vienna University, were looted by the National Socialists with the active participation of employees of Vienna University and later restituted only partially. In the course of the NS provenance research of Vienna University Library the remaining parts of Guido Adler's library could be located. In addition, a partial estate was identified as of doubtful provenance and as belonging to the estate and restituted together with the book holdings in 2012/13. The book contributes to a better understanding of how Vienna University has been dealing with its history by focusing on the case of musicology, provides an example of the reappraisal of the past and of memory work and documents the results of NS provenance research.