  ALICE is a general purpose experiment dedicated to the study of
nucleus-nucleus collisions at LHC. After more than 3 years of successful
operation, an upgrade of the apparatus during the second long shutdown of LHC
(LS2) in 2017/18 is in preparation. One of the major goals of the proposed
upgrade is to extend the physics reach for rare probes at low transverse
momentum. The reconstruction of the rare probes requires a precise
determination of the primary and secondary vertices that is performed in ALICE
by the Inner Tracking System (ITS). The present ITS made of 6 layers of three
technologies of silicon devices allows, for example, to reconstruct D mesons
with the transverse momentum down to ~2 GeV/c.
  Further extension of this range towards lower pT requires the installation of
the new ITS consisting of 7 layers of silicon detectors with significantly
better single point resolution and reduced material budget. It is expected that
the new system will allow to improve the impact parameter resolution by a
factor of ~3. Moreover, the data rate capability of the upgraded ITS should be
significantly improved in order to exploit the full expected LHC lead-lead
interaction rate of 50 kHz, almost two orders of magnitude above the present
readout rate.
  The present contribution describes first the ITS upgrade requirements
followed by the conceptual design of the new system and its expected
performance. Secondly, an overview of the different R&D activities from the
concept towards the final detector is given.
