Short- and long-distance QCD effects in B-meson decays

Various exclusive and inclusive decays of B mesons are studied, at present, with dedicated experiments at ``B factories''. In order to compete with the experimental accuracy, we need a reliable theoretical framework to compute strong interaction effects in a hadronic environment. I discuss how the separation of (perturbatively calculable) short-distance QCD effects from (non-perturbative) long-distance phenomena helps to obtain precise theoretical predictions.