The history of Optimal Transportation is not a long, quiet river. Its birth is commonly dated back to the end of the 18th century, with the problem set by G. Monge in his Mémoire sur la théorie des déblais et des remblais, where the motivation for the problem was the optimal way of moving sand piles for building or military applications. For many modern mathematicians, Monge is the father of OT theory, but his work did not answer to all the questions that we would consider as important issues nowadays, and in particular Monge did not even wonder about a rigorous proof of the existence of an optimizer.A long period of sleep followed, until Kantorovich, who, facing optimization problems related to railway supply chain during World War II, proposed an alternative, relaxed formulation of the transport problem set by Monge. In particular, his work allowed to give both existence and duality results, and paved the way to a modern mathematical treatise of the problem.Initially motivated by those two engineering issues, the problem turned out to be incredibly rich from the mathematical point of view, thereby triggering a huge amount of theoretical questions, some of which are still open. Its connections with many other branches of pure mathematics, and in particular the geometry of manifolds and metric spaces are a very important feature of the theory. In the invited preface by Cédric Villani, the reader will find the point of view on the various topics that are developed in this volume of a mathematician who has been highly involved in the research on these applications to "pure" mathematics.However, in parallel to a huge activity around existence, regularity of transport maps, geometric properties of the Wasserstein space, etc. . . many connections with real world application have surfaced in the last decades. Those links have taken different forms, that we aim at highlighting in the present volume.Firstly, OT has been identified as a natural framework to various existing models (in particular in physics or life sciences), allowing to establish new mathematical properties, or to suggest numerical strategies.In particular, OT allows to study several types of evolution PDEs describing the motion of a density of particles, as it is the case for many (typically parabolic) equations which can be interpreted as gradient flows of suitable energy functionals with respect to optimal transport distances. In [1] the authors study the parabolicparabolic Keller Segel model in chemotaxis via these methods, while in [3] a higher-order optimal transport problem involving gradients is proposed in connection with combinatorics, and a gradient-flow equation is derived from it. Among other models from physics which fit in an OT framework, a very important role is played by the multielectron problems of the Density Functional Theory, which can be interpreted as a multi-marginal Kantorovich problem. In [6] the reader will find new duality results on this model, and in [12] a general introduction to multi-marginal problems and their applicat...