  We have performed the first experimental investigation of quantum
interference corrections to the conductivity of a bilayer graphene structure. A
negative magnetoresistance - a signature of weak localisation - is observed at
different carrier densities, including the electro-neutrality region. It is
very different, however, from the weak localisation in conventional
two-dimensional systems. We show that it is controlled not only by the
dephasing time, but also by different elastic processes that break the
effective time-reversal symmetry and provide invervalley scattering.
