  The High Luminosity Large Hadron Collider (HL-LHC) at CERN is expected to
collide protons at a centre-of-mass energy of 14\,TeV and to reach the
unprecedented peak instantaneous luminosity of
5\,$-$\,7.5\,x\,$10^{34}$\,cm$^{-2}$s$^{-1}$ with an average number of pileup
events of 140\,$-$\,200. This will allow the ATLAS and CMS experiments to
collect integrated luminosities up to 3000\,$-$\,4000\,fb$^{-1}$ during the
project lifetime. To cope with this extreme scenario the CMS detector will be
substantially upgraded before starting the HL-LHC, with a plan known as CMS
Phase-2 upgrade. The CMS Tracker detector will have to be replaced in order to
fully exploit the delivered luminosity and cope with the demanding operating
conditions. The new detector will provide robust tracking as well as input for
the first level trigger. This paper is focused on the replacement of the CMS
Outer Tracker system, describing the new layout and the technological choices
together with some highlights of module assembly and quality assurance aspects.
