Thermalization of QCD plasmas

<!--HTML--><p>Over the past decades experiments at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC) have discovered the formation of a de-confined Quark-Gluon Plasma (QGP) , and established a standard picture of the space-time evolution of the QGP based on relativistic viscous hydrodynamics. While high-energy heavy-Ion collisions thus provide a unique laboratory to study QCD matter under extreme conditions, it has proven challenging to understand how the far-from equilibrium matter created in the collision turns into a nearly equilibrated plasma of quarks and gluons. Starting with a brief introduction, I will highlight recent theoretical progress in understanding thermalization mechanisms in QCD plasmas and address the question how an almost equilibrated Quark-Gluon plasma is created during the early stages of high-energy collisions. I will also discuss how these studies provide new insights into the range of applicability of dissipative fluid dynamics and how an improved understanding of the out-of-equilibrium dynamics of the QGP enables new connections between hot QCD and cold QCD research.</p>