Dynamic response of structures can be analyzed in terms of the propagation of input energy within the structure. Energy propagation is quantified by energy flux (EF), which is the amount of energy transmitted per unit time through a cross section of a medium. The formulation of EF is similar to the formulation of wave propagation in structures. It involves tracking the propagation path of the input energy and the energy loss due to damping within the elements of the structure. The EF approach introduces a new tool to evaluate the dynamic response and the energy absorption capacity of structures, providing an alternative parameter for the design of structures for dynamic loads. This article presents the theoretical basis for the methodology and gives a numerical example for the EF analysis of a plane frame structure under earthquake loads.