  In the high luminosity scenario of the LHC (HL-LHC), which will bring the
instantaneous luminosity up to 7.5\,$\times$\,$10^{34}$\,cm$^{-2}$s$^{-1}$,
ATLAS and CMS will need to operate at up to 200 interactions per 25\,ns beam
crossing and reaching up to 4000\,fb$^{-1}$ of integrated luminosity. To
achieve their physics goals the experiments will need to improve the tracking
and vertexing capability and the ability to selectively trigger on specific
physics events at reasonable thresholds. The upgrade of the CMS Tracker
requires designing new inner and outer tracking detectors to cope with the
increased luminosity and to implement first trigger level functionality. This
paper describes the new layout and the technological choices together with some
highlights of research and development activities.
