This paper presents methods to enhance the punching shear resistance of existing flat slabs (enlargement of supported area, enhancement of flexural resistance of slab, post-installed shear reinforcement and prestressed solutions). In case of post-installed shear reinforcement, systems based on steel and CFRP are mentioned. Static, technological and economic advantages and disadvantages are analysed. Differences between the systems are mainly due to the requirement to access the upper face of the slab, resistance-decrease in case of fire and deformation capacity of the strengthened slab.