Concrete is well known to behave efficiently in fire conditions, as it is incombustible, does not emit smoke, and provides good thermal insulation. Furthermore, in reinforced concrete structures, the concrete cover gives a natural protection to the reinforcement, and the size of the sections often delays the heating of the core, thus favouring the fire resistance of the structural members. In addition, concrete structures are often robust and therefore able to accommodate local damage without major consequences to the overall structural integrity. However, past experience with real fires shows that a thorough understanding of concrete behaviour and structural mechanics is still needed to improve the design of R/C structures with respect to fire. The objective of fib Bulletin 46 is to augment the current knowledge about concrete and concrete structures under fire, not only for the design of new structures, but also for the analysis and repair of existing fire-damaged structures. Both structural and materials issues are examined, and the results of the most recent research activities on the structural performance of concrete subjected to fire are reported. Special attention is paid to the indirect actions caused by the restrained thermal deformations and several basic examples show how a local fire influences global structural behaviour. fib Bulletin 46 is intended for use by practicing engineers to improve their understanding of the behaviour of concrete structures in fire and thereby produce better and safer design standards.