  Quark-Gluon Plasma (QGP), a QCD state of matter created in ultra-relativistic
heavy-ion collisions, has remarkable properties, including, for example, a low
shear viscosity over entropy ratio. By detecting the collection of low-momentum
particles that arise from the collision, it is possible to gain quantitative
insight into the created matter. However, its fast evolution and thermalization
properties remain elusive. Only using high momentum objects as probes of QGP
can unveil its constituents at different wavelengths. In this review, we
attempt to provide a comprehensive picture of what was, so far, possible to
infer about QGP given our current theoretical understanding of jets,
heavy-flavor, and quarkonia. We will bridge the resulting qualitative picture
to the experimental observations done at the LHC and RHIC. We will focus on the
phenomenological description of experimental observations, provide a brief
analytical summary of the description of hard probes, and an outlook on the
main difficulties we will need to surpass in the following years. To benchmark
QGP-related effects, we will also address nuclear modifications to the initial
state and hadronization effects.
