Our unit hosts research on complex systems, that are systems composed of many elements whose mutual interaction gives rise to unexpected emergent phenomena. For example, the behaviour of brain cannot be anticipated from the study of an isolated neuron. Similarly, superconductivity, the ability of some materials to conduct a frictionless electrical current at low temperatures, cannot be anticipated from the study of a single electron. Statistical mechanics, originally developed to study physical systems made of a large number of particles, provides tools and techniques that are well suited to study complex systems and it is a common denominator to many ISC researchers. Yet, the emergence of collective behaviour is certainly not restricted to the physical sciences, but it is ubiquitous in nature, from biology, to social systems and economics. For this reason, the study of complex systems, be it at the theoretical or empirical level, requires a truly interdisciplinary mindset. The great variety of ISC research activities reflects this view of complexity.