  Quantum chromodynamics (QCD) effects in the semileptonic decay b -> c l nu
are evaluated to the second order in the coupling constant, O(alpha_s^2), and
to several orders in the expansion in quark masses, m_c/m_b. Corrections are
calculated for the total decay rate as well as for the first two moments of the
lepton energy and the hadron system energy distributions. Applied to the muon
decay, they decrease its predicted rate by -0.43 ppm.
