Nonleptonic B-decays at NNLO

The decay of B mesons can be predicted within the Heavy Quark Expansion as the decay of a free bottom quark plus corrections which are suppressed by powers of $1/m_b$. This contribution describes the calculation of the NNLO QCD corrections to nonleptonic decays of a free bottom quark including charm quark mass effects. In particular it outlines the challenges in connection to the computation of master integrals, the renormalization of the effective operators and the problems which arise from calculating traces with $\gamma_5$ in $d$ dimensions.