Li survey in giant stars : probing non-standard stellar physics

Lithium has long been known to be a good tracer of non-standard mixing processes occurring in stellar interiors. Here we present the results of a large survey aimed at determining the surface Li abundance in a sample of about 800 giant (RGB and AGB) stars with accurate Hipparcos parallaxes. We compare the observed Li behaviour with that predicted by stellar models including rotation and thermohaline mixing.