Abstract: The Babar detector was a multi-purpose particle physics detector at the PEP-II accelerator in SLAC National Laboratory. It is named after its primary objects of study, the B mesons, and a cartoon elephant. The accelerator was tuned to produce the Upsilon(4S) resonance, which almost always decays into a pair of B mesons. In this talk, I will describe the challenges and methods of searching for events in which a charged B decays into a charged lepton and a neutrino. The primary focus will be the search for charged B mesons decaying into a tau lepton and a neutrino in the recoil of a semi-leptonically decaying B. I will review complementary searches at Babar and the Belle experiment in Japan, and I will present the implications of these results for physics beyond the Standard Model.