Quantum Chromodynamics (QCD) studies the strong nuclear force between quarks mediated by gluons at the core of the Standard Model of particle physics. The nature of QCD leads to complex, fascinating phenomena. The smallest building blocks of matter, quarks and gluons (partons), are usually confined inside protons and neutrons (hadrons). At very high energies, the partons become asymptotically free or deconfined. In QCD, the strong coupling constant “runs” with energy, becoming smaller at high energies. In this regime, QCD is calculable in perturbation theory and known as perturbative QCD (pQCD). In contrast, the strong coupling blows up at smaller energies and becomes non-analytical or non-perturbative QCD (npQCD). In many-body systems, high enough temperatures and energies enable a phase transition to a deconfined state of matter called the Quark-Gluon plasma (QGP).