NLO QCD corrections to top quark pair production and decay at hadron colliders

We present results for the next-to-leading order QCD corrections to the production and semi-leptonic decays of a top quark pair in hadron collisions, retaining all spin correlations. To evaluate the virtual corrections, we employ generalized D-dimensional unitarity. The computation is implemented in a numerical program which allows detailed studies of t (t) over bar -related observables at the Tevatron and the LHC.