Theoretical aspects of the heavy quark expansion

I give a brief outline of the theoretical framework for the modern treatment of the strong interaction effects in heavy quark decays, based on first principles of QCD. This model-independent approach is required to meet the precision of current and future experiments. Applications to a few problems of particular practical interest are reviewed, including the precise determination of Vcb and Vub. I emphasize the peculiarities of simultaneously accounting for the perturbative and power-suppressed effects necessary for accurate predictions.