Jets produced in collisions at the CERN LHC can be reconstructed using the charged-particle tracks measured in the ATLAS Inner Detector. Jets are produced copiously at the LHC, and can be used to study the details of the strong interaction, the hot dense medium produced in heavy ion collisions, and new fundamental particles. Track-based jet measurements complement calorimeter studies, with independent systematic uncertainties. These track jets can be studied down to very low momentum, allowing the emergence of jet structure from soft proton-proton collisions to be observed. Individual particles can be identified, so that the fraction of jet momentum carried by each track may be measured. Results will be shown from data collected in 7 TeV proton-proton collisions, and the role of track jets in the recent ATLAS observation of centrality-dependent dijet asymmetry in lead-lead collisions will be discussed.