A concrete structure without any form of reinforcement will crack and fail when subjected to a relatively small load. The failure occurs suddenly and brittle in most situations. The commonest way to reinforce a concrete structure is to use cast in steel reinforcing bars. Since a concrete structure usually has a very long life, is it not unusual for the demands on the structure to change with time. The structure may have to carry larger loads at a later date or fulfil new standards. In extreme cases a structure will have to be repaired or strengthened due to an accident. Another reason can be that errors have been made during the design or construction phase. There exists several methods to repair or upgrade existing concrete structures. In recent years the development of strong epoxy adhesives has led to the plate bonding repair technique. This technique may be defined as one in which a composite sheet or plate of relatively small thickness is bonded with an epoxy adhesive to, in most cases, a concrete structure to improve its structural behaviour and strength. At Lulea University of Technology, research is taking place in the field of Plate Bonding. The research work started in 1988, then with steel plates and is today continued with FRP (Fibre Reinforced Polymer) materials. Both comprehensive experimental and theoretical work has been undertaken. The laboratory tests include strengthening for bending as well as for shear and torsion. In addition several full-scale tests have been performed over the years. This paper will present two full-scale tests, the first one a road bridge strengthen with steel plates and the second, a rail way bridge strengthen with CFRP (Carbon Fibre Reinforced Polymer) sheets. The tests show that Plate Bonding with steel or CFRP sheets are effective methods to strengthen concrete structures.