Topological source of light: We use rulers and measuring tapes to measure position. The tool to measure time/frequency is a frequency comb that is a light source whose spectrum consists of a series of discrete, equidistant lines. The 2005 Nobel Prize was awarded to scientists who contributed to the development of such a useful tool. Can we miniaturize them and have them one a chip? Unfortunately, any nanofabricated device is prone to defects and damages the quality of the comb. Inspired the concept of topology and the robustness associated to it, a new class of comb is introduced: “topological frequency combs”. These combs could be more efficient than regular ones and more robust against fabrication defects. Mittal et al. Nature Physics 17, 1169 (2021). Contributors: David Lam & Sunil Mittal Mohammad Hafezi