  The cross-section for the production of two jets in association with a
leptonically decaying Z boson ($Zjj$) is measured in proton-proton collisions
at a centre-of-mass energy of 13 TeV, using data recorded with the ATLAS
detector at the Large Hadron Collider, corresponding to an integrated
luminosity of 3.2 fb$^{-1}$. The electroweak $Zjj$ cross-section is extracted
in a fiducial region chosen to enhance the electroweak contribution relative to
the dominant Drell-Yan $Zjj$ process, which is constrained using a data-driven
approach. The measured fiducial electroweak cross-section is
$\sigma^{Zjj}_{EW}= 119\pm 16 (\mathrm{stat.}) \pm 20 (\mathrm{syst.})\pm 2
(\mathrm{lumi.})$ for dijet invariant mass greater than 250 GeV, and $34.2\pm
5.8 (\mathrm{stat.})\pm 5.5 (\mathrm{syst.})\pm 0.7 (\mathrm{lumi.})$ for dijet
invariant mass greater than 1 TeV. Standard Model predictions are in agreement
with the measurements. The inclusive $Zjj$ cross-section is also measured in
six different fiducial regions with varying contributions from electroweak and
Drell-Yan $Zjj$ production.
