  Bilayer graphene (two coupled graphitic monolayers arranged according to
Bernal stacking) is a two-dimensional gapless semiconductor with a peculiar
electronic spectrum different from the Dirac spectrum in the monolayer
material. In particular, the electronic Fermi line in each of its valleys has a
strong p -> -p asymmetry due to a trigonal warping, which suppresses the weak
localization effect. We show that weak localisation in bilayer graphene may be
present only in devices with pronounced intervalley scattering, and we evaluate
the corresponding magnetoresistance.
