The essential features of composite steel concrete beams and slabs are first given for a load bearing mode in one-way bending. The essential features of the two ways acting tensile membrane action load bearing mode are then explained. Experimental tests that helped understanding and quantifying the tensile membrane action, either small scale or large scale, at room temperature or in fire condition, are summarized. Simple calculation models that have been developed for calculating the load bearing capacity of composite floor under fire are presented. Considerations are given about the requirements for numerical models aiming at simulating the behavior of composite floor systems in the fire situation are given. Finally, an application example is presented of a composite floor system designed by the author in 2007.