  Topological photonics is emerging as a new paradigm for the development of
both classical and quantum photonic architectures. What makes topological
photonics remarkably intriguing is the built-in protection as well as intrinsic
unidirectionality of light propagation, which originates from the robustness of
global topological invariants. In this Perspective, we present an intuitive and
concise pedagogical overview of fundamental concepts in topological photonics.
Then, we review the recent developments of the main activity areas of this
field, categorized into linear, nonlinear, and quantum regimes. For each
section, we discuss both current and potential future directions, as well as
remaining challenges and elusive questions regarding the implementation of
topological ideas in photonics systems.
