  The semileptonic decay B -> pi l nu is one of the most important reactions
for the determination of the CKM matrix element |V_{ub}|. However, in order to
extract |V_{ub}| from data one needs an accurate theoretical calculation of the
hadronic matrix element describing the B to pi transition. QCD sum rules, based
on operator-product expansion on the light-cone, provide a reliable approach to
this aim. QCD corrections and higher twist contributions can be taken
systematically into account.
