  A search for the dimuon decay of the Higgs boson was performed using data
corresponding to an integrated luminosity of 36.1 fb$^{-1}$ collected with the
ATLAS detector in $pp$ collisions at $\sqrt{s}=13$ TeV at the Large Hadron
Collider. No significant excess is observed above the expected background. The
observed (expected) upper limit on the cross section times branching ratio is
3.0 (3.1) times the Standard Model prediction at the 95% confidence level for a
Higgs boson mass of 125 GeV. When combined with the $pp$ collision data at
$\sqrt{s}=7$ TeV and $\sqrt{s}=8$ TeV, the observed (expected) upper limit is
2.8 (2.9) times the Standard Model prediction.
