The report deals with the techniques of mortar injection, steel reinforcement and prestressing being used since the 1920s to strengthen old masonry. Due to follow-up examinations of buildings repaired in such manner and with recent research results achieved at the University of Karlsruhe, rules for dimensioning and execution can be made available to practice for the structural repair of old masonry. No universal standards can or should be established for historical buildings, but rules and recommendations can be given for application in practice which can be adapted to the special circumstances of each object.