  We present Gemini and Keck spectroscopic redshifts and velocity dispersions
for twenty clusters detected via the Sunyaev-Zel'dovich (SZ) effect by the
Planck space mission, with estimated masses in the range $2.3 \times 10^{14}
M_{\odot} < M < 9.4 \times 10^{14} M_{\odot}$. Cluster members were selected
for spectroscopic follow-up with Palomar, Gemini and Keck optical and (in some
cases) infrared imaging. Seven cluster redshifts were measured for the first
time with this observing campaign, including one of the most distant Planck
clusters confirmed to date, at $z=0.782\pm0.010$, PSZ2 G085.95+25.23. The
spectroscopic redshift catalogs of members of each confirmed cluster are
included as on-line tables. We show the galaxy redshift distributions and
measure the cluster velocity dispersions. The cluster velocity dispersions
obtained in this paper were used in a companion paper to measure the Planck
mass bias and to constrain the cluster velocity bias.
