  We briefly review advances in understanding the initial stages of a heavy ion
collision. In particular the focus is on moving from parametrizing the initial
state to calculating its properties from QCD, consistently with the description
of hard probes and dilute-dense scattering experiments. Modeling the
event-by-event fluctuating nuclear geometry in initial state calculations has
significantly improved in recent years. We also discuss prospects of directly
seeing effects of particle correlations created in the initial state in the
experimental observables.
