Jet quenching is a unique phenomenon that can occur in relativistic heavy-ion collisions. Jets are produced in both proton-proton and heavy-ion collisions at the LHC. In both collision systems they are produced by two partons, one from each incoming projectile, colliding and exchanging a very large amount of momentum. These partons scatter at a large angle. As they leave the collision region, the scattered parton develops a shower. This is the process by which a colour-charged quark or gluon becomes an observable collection of colour-neutral particles. In proton-proton collisions, this showering process happens in the vacuum, but in nucleus-nucleus collisions, the shower develops inside the QGP. Thus the showering process actually probes the short distance scale properties of the QGP itself. This makes jets one of the most powerful probes of QGP properties.