The Special Issue on the Evolution of Physical Systems describes articles on evolutionary approaches that occur in real-world physical substrates rather than in simulation. Jacobsen and colleagues describe an experimental setup that removes the burden of manually setting the environment from the human supervisor. In their contribution, Scheper and de Croon describe how choosing an appropriate level of abstraction can improve the transfer of evolved solutions across the reality gap. The task domain they have have chosen is a decentralized formation flying task for a group of three small airborne vehicles controlled by neural networks. The work of Vujovic and colleagues is very much in the spirit of this special issue. They introduce a novel robot-building robot composed of a hot-melt extruder and an articulated arm, which acts as a sort of 3D printer, capable of fabricating the legs of simple modular robots. Preen and Bull present an interesting theoretical analysis followed up with an actual physical case study. They employ the abstract NKCS model of coevolution to achieve this. It enables informed sampling of candidate solutions in a coevolutionary scenario. Jelisavcic and colleagues investigate how such a vision could be achieved with a population of robots and 3D printing technology.