  We re-examine the determination of $|V_{cb}|$ from $B\to D \ell \nu$ in view
of recent experimental and theoretical progress, discussing the
parameterization of the form factors and studying the role played by the
unitarity constraints. Our fit to experimental and lattice results for $B\to D
\ell \nu$ gives $|V_{cb}|=40.49(97)\ 10^{-3}$ and to $R(D)= 0.299(3)$.
