Semileptonic B Decays

The following is an overview of the measurements of the CKM matrix elements V_cb and V_ub that are based on detailed studies of semileptonic B decays by the BABAR and Belle Collaborations and recent advances in QCD calculations. In addition, a new and improved measurement of the ratios R(D^(*))= BF(Bbar --> D^(*) tau^- nu_tau)/BF(Bbar -->D^(*) ell^- nu_ell) is presented. Here D^(*) refers to a D or a D^* meson and ell is either e or mu. The results, R(D) = 0.440 +/- 0.058 +/- 0.042 and R(D^*)= 0.332 +/- 0.024 +/- 0.018, exceed the Standard Model expectations by 2.0 s.d. and 2.7 s.d, respectively. Taken together, they disagree with these expectations at the 3.4 s.d. level. The excess of events cannot be explained by a charged Higgs boson in the type II Two-Higgs-Doublet Model.