  Recent measurements of the associated production of two or three massive
vector bosons in proton-proton collisions at the Large Hadron Collider,
collected by the ATLAS detector at a centre-of-mass energy of $\sqrt{s} = 13$
TeV, are reported. The diboson analyses target the production and decay modes
$WW\rightarrow e\nu_e\mu\nu_\mu$, $WZ \rightarrow \ell^{\prime} \nu \ell
\ell\,(\ell = e, \mu)$, $ZZ \rightarrow \ell\ell\nu\nu$, and the $4\ell$ final
state. Fiducial inclusive cross sections are compared to state-of-the-art
Standard Model calculations and several unfolded differential distributions are
measured. In the $WZ$ channel, the helicities of the $W$ and $Z$ bosons are
probed. Results are interpreted in terms of limits on anomalous gauge couplings
in the framework of effective field theories. Finally, the first evidence for
the production of three massive vector bosons ($WWW$, $WWZ$, $WZZ$) is
presented.
