Upgrades of the CMS outer tracker for HL-LHC

The LHC machine is planning an upgrade program which will smoothly bring the luminosity up to or above $5\times 10^{34}$cm$^{-2}$s$^{-1}$ sometimes after 2020, to possibly reach an integrated luminosity of 3000fb$^{-1}$ at the end of that decade. In this ultimate scenario, called Phase-2, when LHC will reach the High Luminosity (HL-LHC) phase, CMS will need a completely new Tracker detector, in order to fully exploit the high-demanding operating conditions and the delivered luminosity. The new Tracker should have also trigger capabilities. To achieve such goals, R and D activities are ongoing to explore options and develop solutions that would allow including tracking information at Level-1. The design choices for the CMS Outer Tracker upgrades are discussed along with some highlights of the R and D activities.