Πάντα χωρεῖ καὶ οὐδὲν μένει
(everything flows and nothing stands still)
Understanding how materials and individuals move, flow, get deformed is certainly not a novel question, but it plays a central role in several major challenges of the XXIst century.
On the one hand, in a world always on the move, mobility issues (whether they deal with pedestrians, vehicles, ...) will, and should, shape our cities and it is therefore a matter of paramount interest to be able to describe and predict the associated traffic. On the other hand, complex materials are abundantly found both in Nature and as synthetic materials, thanks to their peculiar mechanical properties; they are typically deformed and made to flow before they reach their final shapes and will often endure mechanical stresses in their 'lifetime'. Accordingly, better understanding their deformation is often a prerequisite to grasping their global response (for geological flows, earthquakes, ...) or improving their performances (foams with various functionalities, cosmetics, metallic glasses, ...).
On these two topically contrasted fronts, we claim that Physics has its say. Indeed, the way these systems flow results from collective effects that emerge from the interaction of elementary entities, whether they be pedestrians, cars, or elementary material volumes. We strive to understand, describe and model the emergence of the macroscopic properties of these systems, starting from comparatively simple elementary entities that mutually interact. This is achieved by notably leveraging tools from Statistical Physics and exploiting them on a new scientific frontier, while paying due attention to the idiosyncrasies and the specific issues of interest for each of them.