Evolution to the quark–gluon plasma

Theoretical studies on the early-time dynamics in the ultra-relativistic heavy-ion collisions are reviewed, including pedagogical introductions on the initial condition with small-$\text{x}$ gluons treated as a color glass condensate, the bottom–up thermalization scenario, plasma/glasma instabilities, basics of some formulations such as the kinetic equations and the classical statistical simulation. More detailed discussions follow to make an overview of recent developments on the fast isotropization, the onset of hydrodynamics, and the transient behavior of momentum spectral cascades. (key issues review)