Physics prospects for ATLAS at the HL-LHC

The ATLAS experiment at CERN will undergo a series of detector upgrades over the next few years to prepare for the the High-Luminosity Large Hadron Collider (HL-LHC) project. The upgrades are designed to maintain or improve detector performance, even with the instantaneous luminosity needed to deliver a total of 3000 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=14$ TeV to ATLAS. This contribution provides details of the broad and deep program of measurements and searches planned by ATLAS for the HL-LHC. The higher centre-of-mass energy and increased integrated luminosity will allow ATLAS not only to improve the precision of Higgs boson, electroweak boson, and top quark measurements, but also to extend the sensitivity of searches for beyond-the-Standard-Model processes with small cross sections. Many of the projections use detailed detector simulations to model the performance of the proposed ATLAS detector upgrades.