With the remarkable performance of the ATLAS and CMS detectors, jets at the LHC can now be characterized not just by their overall direction and energy but also by their substructure. At the same time, there has been substantial progress in predicting the properties of jets from first principles. In this talk, I highlight the ways that theoretical studies of jet substructure have enhanced our understanding of QCD, including examples that blur the boundary between perturbative and nonperturbative physics.
