In this talk I report on a recent sum rule calculation of the bag parameter for B Bbar mixing. We show that for this particular case the sum rule calculation yields a result with a precision that is competitive to the one of the most recent lattice calculations. The reason for this is that the QCD sum rule computes the deviation of the bag parameter from unity, which is small. Although the QCD sum rule has an accuracy limited to about twenty percent, it is in this case the precision on the deviation form unity. I present the results and compare to the most recent lattice calculations. Finally I present a second result needed to proceed to NNLO precision, which is the calculation of the matching coefficients from QCD to HQET at NNLO.