  The AstroSat satellite is designed to make multi-waveband observations of
astronomical sources and the Cadmium Zinc Telluride Imager (CZTI) instrument of
AstroSat covers the hard X-ray band. CZTI has a large area position sensitive
hard X-ray detector equipped with a Coded Aperture Mask, thus enabling
simultaneous background measurement. Ability to record simultaneous detection
of ionizing interactions in multiple detector elements is a special feature of
the instrument and this is exploited to provide polarization information in the
100 - 380 keV region. CZTI provides sensitive spectroscopic measurements in the
20 - 100 keV region, and acts as an all sky hard X-ray monitor and polarimeter
above 100 keV. During the first year of operation, CZTI has recorded several
gamma-ray bursts, measured the phase resolved hard X-ray polarization of the
Crab pulsar, and the hard X-ray spectra of many bright Galactic X-ray binaries.
The excellent timing capability of the instrument has been demonstrated with
simultaneous observation of the Crab pulsar with radio telescopes like GMRT and
Ooty radio telescope.
