After briefly introducing the basics of some calculation techniques and the model, I will show how a two-Higgs-doublet-model (2HDM) with generic Yukawa structure (type-III) can remove the tension between the Standard Model and the experimental data which was recently reported by Babar Collaboration for the tauonic B decays B -> D\tau\nu and B->D*\tau\nu. I will further show that a 2HDM of type III is also capable of bringing the Standard Model prediction for the branching ratio of B->\tau\nu into an agreement with experiment without violating t'Hooft's naturalness criterion.

Next, taking into account all relevant flavour observables (both tree level and loop processes), I show how the parameter space of the model is constrained. Finally, I will consider lepton flavour observables and show correlations between \mu -> e\gamma and \mu^- -> e^-e^+e^- as well as give upper bounds on the lepton flavour violating B meson decay B_d -> \mu e in the type-III 2HDM.