  This paper presents the specification, design, and development of the Visible
Camera (VIS) on the ESA Euclid mission. VIS is a large optical-band imager with
a field of view of 0.54 deg^2 sampled at 0.1" with an array of 609 Megapixels
and spatial resolution of 0.18". It will be used to survey approximately 14,000
deg^2 of extragalactic sky to measure the distortion of galaxies in the
redshift range z=0.1-1.5 resulting from weak gravitational lensing, one of the
two principal cosmology probes of Euclid. With photometric redshifts, the
distribution of dark matter can be mapped in three dimensions, and, from how
this has changed with look-back time, the nature of dark energy and theories of
gravity can be constrained. The entire VIS focal plane will be transmitted to
provide the largest images of the Universe from space to date, reaching
m_AB>24.5 with S/N >10 in a single broad I_E~(r+i+z) band over a six year
survey. The particularly challenging aspects of the instrument are the control
and calibration of observational biases, which lead to stringent performance
requirements and calibration regimes. With its combination of spatial
resolution, calibration knowledge, depth, and area covering most of the
extra-Galactic sky, VIS will also provide a legacy data set for many other
fields. This paper discusses the rationale behind the VIS concept and describes
the instrument design and development before reporting the pre-launch
performance derived from ground calibrations and brief results from the
in-orbit commissioning. VIS should reach fainter than m_AB=25 with S/N>10 for
galaxies of full-width half-maximum of 0.3" in a 1.3" diameter aperture over
the Wide Survey, and m_AB>26.4 for a Deep Survey that will cover more than 50
deg^2. The paper also describes how VIS works with the other Euclid components
of survey, telescope, and science data processing to extract the cosmological
information.
