Contents 1 Introduction
Any significant understanding of a complex system must rely on system-level descriptions. From human communications to chemical reactions and ecological systems, interactions can often occur in groups of three or more nodes and cannot be described simply in terms of dyads. Networks have emerged as a reference modeling tool for complex systems [1]. Networks are the maps that define the physical or virtual space where interactions take place [3]. Building on earlier work in mathematics, social network analysis and ecology, a handful of breakthrough papers at the turn of the millennium [4], [5] attracted the interest of the scientific community, and triggered thousands of contributions over the next twenty years, culminating into the formation of the new multidisciplinary field of Network Science. This research community has developed an unusual mixture of graph theory [6], [7] and statistical mechanics [8] into a flourishing discipline, with applications spanning the full range of science, from fundamental physics all the way to the social sciences.
