  The planetary system of TRAPPIST-1, discovered in 2016-2017, is a
treasure-trove of information. Thanks to a combination of observational
techniques, we have estimates of the radii and masses of the seven planets of
this very exotic system. With three planets within the traditional Habitable
Zone limits, it is one of the best constrained system of astrobiological
interest. I will review here the theoretical constraints we can put on this
system by trying to reconstruct its history: its atmospheric evolution which
depends on the luminosity evolution of the dwarf star, and its tidal dynamical
evolution. These constraints can then be used as hypotheses to assess the
habitability of the outer planets of the system with a Global Climate Model.
