Hydrodynamic models of ultrarelativistic collisions

We discuss the use of the hydrodynamic model for the description of the evolution of dense matter formed in ultrarelativistic heavy-ion collisions. The collective flow observed in heavy-ion collisions at the BNL Relativistic Heavy Ion Collider and at the CERN Large Hadron Collider is consistent with the assumption that a fireball of strongly interacting matter is formed. Experimental results from p-Pb and d-Au collisions show similar phenomena, which suggests that collective expansion appears in small systems as well. We review the recent application of the hydrodynamic model to small systems and discuss limitations and possible further checks of this scenario.