Freeze-out dynamics in heavy-ion collisions: Recent advances

We briefly review recent advances in the subject of hadron production in relativistic heavy ion collisions. We focus on the issues of chemical freeze-out, chemical equilibration and the role of post-hadronization inelastic collisions. From the observations collected in elementary and heavy ion collisions, a picture emerges in which hadrons are born in chemical equilibrium at hadronization, thereafter undergoing inelastic and elastic collisions whose impact on the primordial distribution depends on the system size.