Using a hexagonal array of helical waveguides, physicists have observed robust optical waves that move in one direction, bypassing obstacles and imperfections exactly as predicted by the theory of topological insulators. See Letter p.196 One of the hottest fields of condensed-matter research is that of topological insulators. They exist in electronic states that are robust against disorder owing to the topological protection provided by the underlying electronic structure. Their potential practical importance lies in their ability to control and manipulate electron waves without scattering. An interesting question is whether it would be possible to make a topological insulator for light. The answer is yes, and here Mordechai Segev and colleagues demonstrate the first experimental realization of a photonic topological insulator, which consists of helical waveguides arranged in a honeycomb lattice. The helicity is crucial, providing a symmetry breaking effect leading to topological insulator properties. The authors demonstrate one-way edge states that are protected from scattering.