  Before the publication of the Gaia Catalogue, the contents of the first data
release have undergone multiple dedicated validation tests. These tests aim at
analysing in-depth the Catalogue content to detect anomalies, individual
problems in specific objects or in overall statistical properties, either to
filter them before the public release, or to describe the different caveats of
the release for an optimal exploitation of the data. Dedicated methods using
either Gaia internal data, external catalogues or models have been developed
for the validation processes. They are testing normal stars as well as various
populations like open or globular clusters, double stars, variable stars,
quasars. Properties of coverage, accuracy and precision of the data are
provided by the numerous tests presented here and jointly analysed to assess
the data release content. This independent validation confirms the quality of
the published data, Gaia DR1 being the most precise all-sky astrometric and
photometric catalogue to-date. However, several limitations in terms of
completeness, astrometric and photometric quality are identified and described.
Figures describing the relevant properties of the release are shown and the
testing activities carried out validating the user interfaces are also
described. A particular emphasis is made on the statistical use of the data in
scientific exploitation.
