Is there a systematic way to minimize the weight of car and aeroplane parts? Is there a way to design materials that expand transversely when pulled? To design materials that shrink when heated? To design robots that are so small that they can be mounted on the head of a pin? The answer to all four questions is affirmative; the method that solves the problems is called ‘topology optimization’. This method is based on complex computer calculations. This paper describes the background of the method and shows a number of applications, ranging from the design of materials with ‘exotic’ properties over microscopic robots to the design of large–scale satellite structures.