  A sizeable charge asymmetry in top quark pair production has been observed at
the Tevatron. The experimental results seem to exceed systematically the
Standard Model theory predictions by a significant amount and have triggered a
large number of suggestions for 'new physics'. The effect is also visible at
the LHC, and preliminary results have already been presented by the ATLAS and
CMS collaborations. In this talk, we review the present status of the
theoretical predictions, and their comparison with the experimental
measurements.
