  Gaia mission will offer an exceptional opportunity to perform variability
studies. The data homogeneity, its optimised photometric systems, composed of
11 medium and 4-5 broad bands, the high photometric precision in G band of one
milli-mag for V=13-15, the radial velocity measurements and the exquisite
astrometric precision for one billion stars will permit a detailed description
of variable objects like stars, quasars and asteroids.
  However the time sampling and the total number of measurements change from
one object to an other because of the satellite scanning law. The data analysis
is a challenge because of the huge amount of data, the complexity of the
observed objects and the peculiarities of the satellite, and needs a thorough
preparation.
  Experience can be gained by the study of past and present survey analysis and
results and Gaia should be put in perspective with the future large scale
surveys, like Pan-STARRS or LSST.
  We present the activities of the Variable Star Working Group and a general
plan to digest this unprecedented data set, focusing here on the photometry.
