  We present a detailed study of non-leptonic two-body decays of B mesons based
on a generalized factorization hypothesis. We discuss the structure of
non-factorizable corrections and present arguments in favour of a simple
phenomenological description of their effects. We discuss tests of the
factorization hypothesis and show how it may be used to determine unknown decay
constants. In particular, we obtain f_{D_s}=(234\pm 25) MeV and
f_{D_s^*}=(271\pm 33) MeV.
