Synthetic reinforcement in asphalt pavements has been used in Norway for about 25 years. Mainly it has been used in connection with repaving of road sections with severe cracking problems. The principal reasons for cracking of asphalt overlays are frost heave, traffic induced rutting due to plastic deformations in granular layers and differential settlements in the base layers and in the subgrade. The evaluation of when and how to use reinforcement should be based on the appearing degradation mechanisms. As the governing mechanisms depend on plastic deformations, it is useless to evaluate beneficial effects of the reinforcement by the use of elastic properties. As a general rule reinforcement should primarily be used to improve service lifetime and not to reduce overlay thickness. Correct installation of the reinforcement is crucial for the result.