We are delighted to introduce this Special Issue on the Evolution of Physical Systems, the culmination of a series of workshops organized around the topic that began with ALIFE XIII (2012) and ran through ECAL 2013, ALIFE XIV (2014) and ECAL 2015. Inspired by our mutual interests, we coined the term Evolution of Physical Systems (EPS) to describe evolutionary approaches that occur in real-world physical substrates rather than in simulation. We deliberately chose this term to be broad enough to encompass both parallel Embodied Evolution [19], in which evolution is distributed across a population of robots, as well as more classical Evolutionary Robotics work where evaluation is serialized on a single robot, such as Floreano and Mondada [5].