This paper reviews the current understanding of the characteristics of structural steels at elevated temperatures typical of those experienced in a fire and the design of fire-resistant steels for building construction. Following a commercial view of the requirements and market for steels with enhanced properties at elevated temperatures, the microstructure/property relationships and the influence of these upon high temperature strength are discussed in detail. Steel composition and processing variables can be controlled to modify grain size, the presence of second phases and precipitation, ferrite/austenite transformation temperature, dislocation density and weldability. These are reviewed as well as the important issues concerning structural aspects that determine the fire resistance of steels. The microstructure and property requirements of fire resistant steels are outlined and the ways in which these may be achieved are discussed including those that have already been developed.