QCD is the theory that describes the strong force. One of its features is that its Lagrangian is written in terms of quarks and gluons, degrees of freedom that are never observed in isolation. Instead, we observe hadrons, the bound states that they form. However, at high temperatures, a quark-gluon plasma (QGP) is formed. In this phase quarks and gluons are not confined within hadrons. The QGP, that was present in the early universe, can only be observed in heavy-ion collisions nowadays. One of the observables that allows obtaining more information about the QGP is heavy quarkonium suppression. Heavy quarkonium is a bound state formed by two heavy quarks. It can only be formed at the beginning of the collision due to the high energy that is required. However, it can melt due to the interaction with the medium that appears afterwards. Comparing quarkonium production in heavy-ion collisions with results on proton-proton collisions we can deduce properties of the QGP. In this talk, I will review the motivation to study heavy-ion collisions and quarkonium suppression. I will explain how the non-relativistic nature of quarkonium can be exploited using Effective Field Theories and how this has improved our understanding in the last years. Finally, I will review recent efforts to compute the suppression pattern which combine the use of Effective Field Theories with the framework of Open Quantum Systems.