The ground state of the Higgs potential is found at a non-zero value of the Higgs field. This spontaneously breaks the electroweak symmetry, generating masses for most Standard Model particles. The shape of the Higgs potential is determined by the Higgs boson self-coupling, which can be probed through the pair production of Higgs bosons. This proceeding reports results for the latest $HH$ searches by the ATLAS experiment in the $b\bar{b}\gamma\gamma$, $b\bar{b}\tau^+\tau^-$, and $b\bar{b}b\bar{b}$ decay channels. These are obtained from the full LHC Run 2 dataset with $\sqrt{s}=13$ TeV $pp$ collisions. Non-resonant $HH$ results are interpreted as constraints on the Higgs boson self-coupling as well as upper limits on the Standard Model signal strength. Limits are also set on heavy resonances decaying to Higgs boson pairs.