The discovery of topological phases and topological insulators has revolutionized several fields of natural sci-ence, including condensed matter physics, materials sci-ence, and photonics. Topological concepts have been implemented in a variety of materials and in a broad range of wave systems ranging from electronic, atomic, photo-nic, plasmonic, polaritonic, to microwave, acoustic, and mechanical waves. About a dozen years ago, the concept of quantum Hall effect and topological insulators was introduced to the realm of photonics1, and the idea was soon demonstrated in a gyromagnetic photonic crystal2. Several years later, photonic topological insulators mani-fested as topologically protected edge states were realized in several pioneering experiments performed using dif-ferent photonic systems3–8. Much of the topological fea-ture of Bloch bands is revealed in momentum space, using the concepts such as the Chern number and Berry phase (as illustrated in the cover figure of this feature collection). By now, there have been numerous theoretical and experimental efforts in the study of nontrivial topological photonic systems, from fundamentals to applications, turning it into an ever-burgeoning research field of topological photonics9–11. Indeed, research activities on topological photonics have grown tremendously in the past decade, with numerous progress made in imple-menting topological phases of light using different plat-forms such as metamaterials, surface plasmons, exciton-polaritons, photonic crystals, waveguide lattices, and coupled cavities9–14. New findings and discoveries emerge rapidly in topologically protected edge states and corner states, topological phases in synthetic dimensions, high-dimensional topological insulators, nonlinear effects in topological systems, non-Hermitian topological photonics and quantum phenomena, and particularly, in the topo-logical insulator lasers15–24.