Femtoscopy at the LHC

We discuss the results of femtoscopic correlations performed by various experiments at the Large Hadron Collider and theoretical efforts to interpret them. Two-particle low relative momentum correlations are used to measure the size of the region emitting particles in nuclear collisions. In pp collisions it is important to test the spatio-temporal characteristics of particle production at small scales. The results are compared to sizes measured in Pb+Pb collisions, as a function of pair momentum and centrality. They are interpreted in the frame of hydrodynamic models and used to test the hypothesis of the collective behavior of matter in such collisions