The efficient use of materials is of great importance, and the choice of the basic topology for the design of structures and mechanical elements is crucial for the performance of sizing of shape optimization. This volume provides a comprehensive review of the state of the art in topology design, spanning fundamental mathematical, mechanical and implementation issues. Topology design of discrete structures involves large scale computational problems and the need to select structural elements from a discrete set of possibilities. The formulation and solution of discrete design problems are described, including new applications of genetic algorithms and dual methods. For continuum problems the emphasis is on the `homogenization method', which employs composite materials as the basis for defining shape in terms of material density, unifying macroscopic structural design optimization and micromechanics. All aspects of this field are covered, including computational aspects and the use of the homogenization method in a computer-aided design environment.