The Society of St. Charles Borromeo (Borro-Mäusverein) is a German Catholic association for the encouragement and diffusion of edifying, instructive, and entertaining literature.
It ran a book club, and free reading rooms in large cities.
From 1902 the society issued a periodical, originally called Borro-mäusblätter, later Die Bücherwelt.
Johannes von Geissel, Philipp Krementz, and Hubert Theophil Simar did much to further its aims, and it spread all over Germany.
The society was able to supply its members with a large number of books at a reduced price, often not more than two-thirds of the ordinary cost of the volumes.