On three-body B decays to charm

I briefly describe the use of the three-body decay modes $B^0 \to D^{(*)-} D^{(*)0} K^+$ to investigate open issues in charmed meson spectroscopy, and of the time dependent $B^0 (\bar {B^0}) (t) \to D^{-} D^{+} \pi^0$ transitions for a measurement of $\cos (2 \beta)$.