Recent experiments on large chains of Rydberg atoms [H. Bernien et al., arXiv:1707.04344] have demonstrated the possibility of realizing 1D systems with locally constrained Hilbert spaces, along with some surprising signatures of non-ergodic dynamics, such as persistent oscillations following a quench from the Neel product state. I will argue that this phenomenon is a manifestation of a "quantum many-body scar", i.e., a concentration of extensively many eigenstates of the system around special many-body states. The special states are analogs of unstable classical periodic orbits in the single-particle quantum scars. I will present a model based on a single particle hopping on the Hilbert space graph, which quantitatively captures the scarred wave functions up to large systems of 32 atoms. These results suggest that scarred many-body bands give rise to a new universality class of quantum dynamics, which opens up opportunities for creating and manipulating novel states with long-lived coherence in systems that are now amenable to experimental study.