  I present the results of first principles calculations of the phonon
dispersions and electron-phonon coupling for BaTi$_2$Sb$_2$O. The phonon
dispersions show a weak lattice instability near the zone corners that leads to
a charge-density wave phase. The calculations of the electron-phonon coupling
reveal strong coupling, especially to the in-plane Ti modes. The total coupling
is large enough to readily explain the superconductivity in this compound. As
the Fermi surfaces are disconnected with different orbital character weights,
this compound is likely to host a multiband superconductivity.
