Abstract: The Moiré phenomenon refers to the formation of a superlattice with a larger period in space when two periodic structures with slightly mismatched periods or orientations are superimposed, resulting in a Moiré pattern. In condensed matter physics, it has been demonstrated as a crucial means for realizing flat-band and strongly correlated quantum states. Recently, this concept has been extended to optical systems, generating a new class of engineered optical structures: Moiré photonic crystals. Through interlayer mismatch, relative twist, or periodic perturbations, these structures can significantly suppress photon kinetic energy while preserving overall spatial symmetry. This leads to the formation of nearly dispersionless optical flat bands and enables strong light field localization in real space. This paper provides a review of the formation and flat band physics of such photonic crystals, and also outlines recent advances in the application of Moiré photonics to cavity quantum electrodynamics systems, low-threshold nanolasers, polariton condensation, and the enhancement of nonlinear optical processes.