  Hadronic decays of $B$ mesons are reviewed. First, masses of $B$ mesons and
observed patterns together with physics behind them are discussed. Then the
effective Hamiltonian responsible for major decays is presented and its
practical applications are discussed in the context of factorization. Various
tests of factorization are then studied. For rare decays, the focus is placed
on $K\pi$, $\pi\pi$ final state and the penguin-mediated $X_s\gamma$. In
general, the measurements are in excellent agreement with predictions of the
standard model.
