  Perturbative and nonperturbative QCD corrections to semileptonic B decay
rates are calculated and given in analytical and numerical forms. We present
the analytic expression for the double distribution in hadronic mass and
electron energy in B to X(u) e nu_e decays through one loop order of QCD. We
then study the leading twist corrections to that quantity within the formalism
of HQET and employ it in a proposed method of measuring V_ub with an accuracy
of 10%. Our other point of interest is the polarisation of the tau lepton in B
to X(c) tau nu_tau processes. Analytic formulae are given for the one-loop QCD
correction to the longitudinal polarisation. The resulting moments of
distributions are discussed, incorporating the HQET corrections found by Falk
et al. The polarisation receives only a very small perturbative correction. It
can be used in extracting the quark masses. Experimental considerations led us
to the calculation of corrections to the polarisation of tau with respect to
the momentum of the virtual $W$ boson. Analytical results for the O(1/m_b^2)
terms have been combined with numerically evaluated perturbative contributions
to give the corrected polarisation.
