Theory of Nonleptonic B Decays

I briefly review some recent progress in the theory of nonleptonic B decays. After introducing the operator product expansion and the relevant effective Hamiltonian, I discuss the domain of validity and the theoretical justification of the factorization approximation and of its generalizations. Furthermore, I review some general parameterizations of B decay amplitudes: the "diagrammatic" approach and the formalism based on Wick contractions in the matrix elements of four-fermion operators.