Searches for Dark Matter produced in association with a Higgs boson and invisible decays of the observed Higgs boson using the ATLAS detector

In the Standard Model, the branching ratio for Higgs boson decays to invisible final states is very small, but it can be significantly enhanced in extensions of the Standard Model. In addition, the observed Higgs boson could couple to new particles decaying into Dark Matter. This talk presents searches for Higgs boson decays to invisible final states or Dark Matter in association with the observed Higgs boson using the full Run 2 data recorded with the ATLAS detector.