During the last ten years a rapid progress has been made in the development of analytical methods for a fire engineering design of load bearing structures and structural members. In a longterm perspective, the development then goes towards an analytical design, directly based on a natural fire exposure, specified with regard to the combustion characteristics of the fire load and the geometrical, ventilation and thermal properties of the fire compartment. This progress is now followed up by a further development towards a reliability based structural fire engineering design. Internationally, the development includes contributions, related to a probabilistic approach on level I, based on a system of partial safety coefficients, as well as to a probabilistic approach on level II, based on the safety index concept. The paper describes and comments on these parallel developments with special reference to fire exposed reinforced concrete structures.