  We evaluate the decay constants for the B and $D$ mesons and the form factors
for the semileptonic decays of the B meson to $D$ and $D^*$ mesons in a
Bethe-Salpeter model. From data we extract $V_{cb}=0.039 \pm 0.002$ from ${\bar
B} \to D^* l {\bar{\nu}} $ and $V_{cb}=0.037 \pm 0.004$ from ${\bar B} \to D l
{\bar{\nu}} $ decays. The form factors are then used to obtain non-leptonic
decay partial widths for $ B\to D \pi (K) $ and $B \to D D (D_s) $ in the
factorization approximation.
