Topological photonic crystals: The application of topology in optics has led to a new paradigm in developing photonic devices with robust properties against disorder. Although considerable progress on topological phenomena has been achieved in the classical domain, the realization of strong light-matter coupling in the quantum domain remains unexplored. We experimentally demonstrated a strong interface between single quantum emitters and topological photonic states. Our approach created robust counterpropagating edge states at the boundary of two distinct topological photonic crystals. This approach may enable the development of quantum optics devices with built-in protection, with potential applications in quantum simulation and sensing. Barik et al. Science 359, 666(2018). Contributors: Emily Edwards & Sabyasachi Barik, Mohammad Hafezi, Edo Waks