  zCOSMOS is a large redshift survey that is being undertaken in the COSMOS
field using 600 hours of observation with the VIMOS spectrograph on the 8-m
VLT. The survey is designed to characterise the environments of COSMOS galaxies
from the 100 kpc scales of galaxy groups up to the 100 Mpc scale of the cosmic
web and to produce diagnostic information on galaxies and active galactic
nuclei. The zCOSMOS survey consists of two parts: (a) zCOSMOS-bright, a
magnitude-limited I-band IAB < 22.5 sample of about 20,000 galaxies with 0.1 <
z < 1.2 covering the whole 1.7 deg2 COSMOS ACS field and designed to mimic the
parameters of the 2dfGRS; and (b) zCOSMOS-deep, a survey of approximately
10,000 galaxies selected through colour-selection criteria to have 1.4 < z <
3.0, within the central 1 deg2. This paper describes the survey design and the
construction of the target catalogues, and briefly outlines the observational
program and the data pipeline. In the first observing season, spectra of 1303
zCOSMOS-bright targets and of 977 zCOSMOS-deep targets have been obtained.
These are briefly analysed to demonstrate the characteristics that may be
expected from zCOSMOS, and particularly zCOSMOS-bright, when it is finally
completed between 2008-2009. The power of combining spectroscopic and
photometric redshifts is demonstrated, especially in correctly identifying the
emission line in single-line spectra and in determining which of the less
reliable spectroscopic redshifts are correct and which are incorrect. Our
zCOSMOS-deep spectra demonstrate the effectiveness of our selection techniques
to isolate high redshift galaxies at 1.4 < z < 3.0 and of VIMOS to measure
their redshifts using ultraviolet absorption lines.
