Abstract: This paper summarizesthe authors' recent developments in ESO and bi-directional ESO(BESO), from the theoretical validation of the method, itsapplications in a variety of design optimization problems ofcontinuum structures, to computer software realization of topologyoptimization. The results clearly demonstrate the capability ofESO/BESO for solving a wide range of engineering design problemsand its easy accessibility through well-established CADenvironments to design practice of architecture and machinery.