With the view that a complex system includes “any object whose behavior as a whole is not determined in a simple way by the behavior of its individual constituents”, the Complex Systems Academy covers a broad spectrum of scientific activities that often cross conventional scientific fields. Following the first two years of existence of the Academy, this edition of the Proceedings of the Complex Systems Academy of Excellence was prepared in the wake of the first “Complex Days” Academy-wide meeting, which took place in Nice in January 2018. As such, this book is a nonexclusive window into the many research topics that are currently addressed at the Université Côte d’Azur within the scope of the Academy. Far from being an exhaustive list or final word, it is only a glimpse of the ongoing research at a very precise point in time. Still, as will be evident to the reader, many topics are discussed in the following chapters, ranging from mathematics and physics to archeology, chemistry and space science or ecology and biophysics. Can such a diversity be categorized? Would it even be really productive at the time of writing? Inspired by one of the most emblematic phenomena encountered in complex systems, namely “self-organization”, the organizers of the meeting and the editors of this compendium deliberately decided not to categorize. Instead, the choice was to mix topics as much as possible and to leave the reader to construct from the parts his or her own vision of the whole, free from disciplinary silos.