Jet substructure is a versatile tool that has been widely used to tag different types of jets, enabling new searches and measurements at the LHC. While its use for tagging has been broadly explored, it is also sensitive to QCD across a wide range of scales, and can be used to understand parton showers and hadronization. Theoretical advances have made it possible to analytically predict the behavior of certain types of substructure observables, and when coupled with experimental measurements, these predictions enable new tests of QCD. This talk will discuss different jet substructure measurements using the ATLAS detector, including measurements of the jet mass and the Lund jet plane, covering experimental challenges and comparisons to theoretical predictions. This talk will also address future applications of this work, as well as experimental areas of development which will increase the potential for substructure at the LHC and beyond.