One of the major concerns in the structural engineering practice is to assess the nonlinear response of new or existing structures for moderate or strong earthquake motions in a simple way. This can be done using what the author defines as displacement ductility demand spectrum (DDDS). This DDDS is a variation of the well-known nonlinear response spectrum for single degree of freedom (SDOF) systems with fixed displacement ductility demands. The proposed spectra and their applications for the seismic evaluation of structures are illustrated for different structural systems that the author has previously evaluated using other methods.