Perturbative QCD analysis of exclusive $B$ meson decays

We review the perturbative QCD formalism for exclusive heavy meson decays, concentrating on the three-scale factorization theorem for nonleptonic processes. The formalism is then extended to the radiative decay $B\to K^*\gamma$, which occurs through penguin diagrams. It is observed that the contributions from the operators other than the penguin one $b\to s\gamma$ are not negligible. From the best fit to the experimental data of the branching ratio ${\cal B}(B\to K^*\gamma)$, we extract the $B$ meson wave function, which possesses a sharp peak in the region with a small momentum fraction.