Some considerations are presented on the main steps followed in the structural repair of monumental buildings. Anamnesis, <i>in situ</i> tests, diagnosis, therapy, and continuous check are illustrated with special reference to old masonry buildings. Recent experimental and numerical techniques for the non-destructive characterization of material properties and for the determination of <i>in situ</i> stresses are discussed. Various criteria are compared for the choice of structural repairs. -- AATA