  Decays of B mesons into final states containing a tau lepton are sensitive to
new charged-current interactions that break lepton-flavor universality. These
decays have been studied only at e+e- colliders, where the low-background
environment and well-known initial state make it possible to observe small
signals with undetectable neutrinos. In particular, the large data samples of
the B factories and recent advances in techniques for full-event reconstruction
have led to evidence for the decay B --> tau nu and unambiguous observation of
the decays B --> D(*)tau nu. These results have led to exclusion of large
regions of the parameter space for a variety of new-physics models.
Furthermore, the branching fraction for B --> D(*)tau nu has been measured to
be higher than the standard-model expectation by at least 3.4 standard
deviations, making this an interesting topic for further research. This letter
reviews the theoterical and experimental status of this topic, summarizing the
results at this time and outlining the path for further improvements.
