QCD factorization for exclusive, non-leptonic B decays

Exclusive, non-leptonic, two-body decays of B mesons simplify greatly in the heavy quark limit. In this talk I discuss the factorized structure that holds in this limit and some of its consequences: (a) naive factorization is recovered in a certain limit; (b) `non-factorizable' effects are hard and can be calculated; (c) strong interaction phases vanish in the heavy quark limit (and can be calculated as well). As an illustration, I compute the penguin contribution to the decay $B_d\to\pi^+\pi^-$ and its effect on the determination of $\sin 2\alpha$.