The advancement of nanotechnology has enabled unprecedented manipulation of light and control over its interaction with matter in various engineered photonic/plasmonic metastructures. This session focuses on the fundamental physics and numerical modeling of light-matter interaction in practical photonic/plasmonic meta-structures, leading to the enhanced performance metrics and new applications of metamaterials, metasurfaces, metallic and dielectric nanoantennas, and plasmonic nanostructures. Example topics include light-matter interaction in strong coupling regime, nonlinear optics in photonic/plasmonic meta-structures, novel optical devices, polariton lasers, single-photon sources, light-emitting metasurfaces, quantum plasmonics, random lasers, lasing spasers, etc.