The lifetime splitting between the B and B d mesons has recently been calculated in the next-to-leading order of QCD. These corrections are necessary for a reliable theoretical prediction, in particular for the meaningful use of hadronic matrix elements computed with lattice QCD. Using results from quenched lattice QCD we find τ (B)/τ (B d) = 1.053 ± 0.016 ± 0.017, where the uncertainties from unquenching and 1/mb corrections are not included. The lifetime difference of heavy baryons Ξ0b and Ξ − b is also discussed. Invited talk at Continuous Advances in QCD 2002/ARKADYFEST (honoring the 60th birthday of Prof. Arkady Vainshtein), 17-23 May 2002, Minneapolis, Minnesota, USA. Fermilab is operated by URA under DOE contract No. DE-AC02-76CH03000.