  ALICE (A Large Ion Collider Experiment) is the CERN LHC experiment optimized
for the study of the strongly interacting matter produced in heavy-ion
collisions and devoted to the characterization of the Quark-Gluon Plasma. To
achieve the physics program for LHC Run 3 and 4, ALICE is undergoing a major
upgrade of the experimental apparatus during the ongoing second long LHC
shutdown. A key element of the ALICE upgrade is the substitution of the Inner
Tracking System (ITS) with a completely new silicon-based detector whose
features will allow the reconstruction of rare physics channels which could not
be accessed before with the ITS layout used during LHC Run 1 and 2. The
enabling technology for such performance boost is the adoption of
custom-designed MAPS (Monolithic Active Pixel Sensors) as detecting element. In
this proceedings, the status of the construction and commissioning of the ITS
upgrade will be detailed. The completion of the modules construction will be
achieved soon and, in the meantime, the commissioning in laboratory is
proceeding using the components already integrated in the detector.
