In Compression Shear Tests (CST) specimens of Laminated Safety Glass (LSG) are inserted in a special test device with an angle of 45° with respect of the loading force so that the compression and the shear components acting in the plane of the plastic interlayer have always the same magnitude. The CST procedure has been adopted in the present research in order to assess the ultimate shear stresses of PVB interlayers of different kinds. Critical values of shear and normal stresses have been taken as measures of the adhesion properties of PVB to be implemented in calculations to model interfacial adhesion. Different sets of specimens were prepared under different bond process conditions and tested at the Laboratory for Testing Materials and Structures of the University of Pisa. The shear viscoelastic properties, as creep and relaxation, have been investigate on large specimens restrained by a eight point fixing. A numerical viscoelastic model of LSG was adopted to compare the FEM predictions with experimental results.