  The first collisions of lead nuclei, delivered by the CERN Large Hadron
Collider (LHC) at the end of 2010, at a centre-of-mass energy per nucleon pair
$\sqrt{s_{NN}}$ = 2.76 TeV, marked the beginning of a new era in
ultra-relativistic heavy-ion physics. The study of the properties of the
produced hot and dense strongly-interacting matter at these unprecedented
energies is currently experimentally pursued by all four big LHC experiments,
ALICE, ATLAS, CMS, and LHCb. The more than a factor 10 increase of collision
energy at LHC, relative to the previously achieved maximal energy at other
collider facilities, results in an increase of production rates of hard probes.
This review presents selected experimental results focusing on observables
probing hard processes in heavy-ion collisions delivered during the first three
years of the LHC operation. It also presents the first results from Run 2
heavy-ion data at the highest energy, as well as from the studies of the
reference pp and pPb systems, which are an integral part of the heavy-ion
programme.
