The importance of the geometric layout in multi physical settings are crucial to the performance of these devices. This holds for many problems covering several different physical disciplines, e.g. fluid-structure interaction in aerospace applications, thermal transport in fluids for cooling or heat-exchange, acoustic-mechanical coupling in micro-acoustic devices such as hearing aids, and many other areas. Often the interface on which the physics couple are paramount, and hence, special attention must be given to ensure a will-defined boundary. This presentation will present several approaches for a variety of different coupled physics problems. That is, the density method is great for some problems, while for other problems pure, or generalized, shape optimization is a better choice. In other words, don’t use a saw to hammer in nails. A hammer is a much better tool in this task. The presentation will cover density methods for thermal transport, pure shape for micro-acoustic problems with visco-thermal losses and parametric level set methods for acoustic-structure interaction problems. Several numerical examples will be presented and the weakness and strength of the different design methods will be discussed.