  The ALICE detector was designed to track and identify particles in a wide
transverse momentum range, from more than 100 GeV/c down to ~100 MeV/c. The
innermost barrel-like detector, the Inner Tracking System (ITS), is dedicated
to precise tracking and to primary and secondary vertices reconstruction. In
this proceeding we present the ITS performance for tracking, primary vertex
reconstruction and particle identification capability. The current
understanding of the detector response is the result of an extensive phase of
commissioning started with 2008 cosmic-ray run and finalized with data from pp
collisions: the alignment status of the three ITS sub-systems (Silicon Pixel
Detectors, Silicon Drift Detectors, Silicon Strip Detectors) and the study of
the detector material budget via the reconstruction of gamma conversion in the
material are presented. Precise tracking is required to reconstruct and
separate the primary vertex of interaction from secondary vertices from
hyperons and heavy-flavour meson decays: some examples of the achieved results
are shown.
