  The WZ production cross section is measured in proton-proton collisions at a
centre-of-mass energy $\sqrt{s} =$ 13 TeV using data collected with the CMS
detector, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The
inclusive cross section is measured to be $\sigma_{\text{tot}}$(pp $\to$ WZ$)$
= 48.09 $^{+1.00}_{-0.96}$ (stat) $^{+0.44}_{-0.37}$ (theo) $^{+2.39}_{-2.17}$
(syst) $\pm$ 1.39 (lumi) pb, resulting in a total uncertainty of
$-$2.78/$+$2.98 pb. Fiducial cross section and ratios of charge-dependent cross
section measurements are provided. Differential cross section measurements are
also presented with respect to three variables: the Z boson transverse momentum
$p_\mathrm{T}$, the leading jet $p_\mathrm{T}$, and the $m$(WZ) variable,
defined as the invariant mass of the system composed of the three leptons and
the missing transverse momentum. Differential measurements with respect to the
W boson $p_\mathrm{T}$, separated by charge, are also shown. Results are
consistent with standard model predictions, favouring
next-to-next-to-leading-order predictions over those at next-to-leading order.
Constraints on anomalous triple gauge couplings are derived via a binned
maximum likelihood fit to the $m$(WZ) variable.
