  During the Long Shutdown 2 of the LHC in 2018/2019, the ALICE experiment
plans the installation of a novel Inner Tracking System. It will replace the
current six layer detector system with a seven layer detector using Monolithic
Active Pixel Sensors. The upgraded Inner Tracking System will have
significantly improved tracking and vertexing capabilities, as well as readout
rate to cope with the expected increased Pb-Pb luminosity of the LHC. The
choice of Monolithic Active Pixel Sensors has been driven by the specific
requirements of ALICE as a heavy ion experiment dealing with rare processes at
low transverse momenta. This leads to stringent requirements on the material
budget of 0.3$% X/X_{0}$ per layer for the three innermost layers. Furthermore,
the detector will see large hit densities of $\sim 19
\mathrm{cm}^{-2}/\mathrm{event}$ on average for minimum-bias events in the
inner most layer and has to stand moderate radiation loads of 700 kRad TID and
$1\times 10^{13}$ 1 MeV n$_\mathrm{eq}/\mathrm{cm}^{2}$ NIEL at maximum. The
Monolithic Active Pixel Sensor detectors are manufactured using the TowerJazz
0.18 $\mu$m CMOS Imaging Sensor process on wafers with a high-resistivity
epitaxial layer. This contribution summarises the recent R&D activities and
focuses on results on the large-scale pixel sensor prototypes.
