The COST action Black holes in a violent universe The interest of scientist in black holes is not limited to their role in the general theory of relativity. The fundamental questions about how black holes are created, their evolution and, possibly, their end are still widely open. Unfortunately, a system which by denition is able to entrap the light, if it passes close enough to its center, can hardly be expected to provide much information to an observer. From the outside, one can only infer the mass, the angular momentum and the electric charge of a black hole, because these are the parameters which describe how it interacts with the universe beyond its event horizon. The attention of researchers, then, is mainly focused on the way black holes in uence the surrounding environment. Given the extreme nature of these objects, the physical processes which bound the black holes with their environment are also extreme. The amount of energy required for the creation of black holes is enormous, such that the scale of energy accessible through the Large Hadronic Collider (LHC) ___ at present, the most powerful particle accelerator in the world ___ may not even be enough to create quantum black holes. The study of black holes is a look pointed towards the most extraordinary physical conditions which nature discloses. To support this study, in the whole variety of its aspect, is the aim of the COST action Black holes in a violent universe, presented in these pages.