In recent modern optics, two rapidly developing branches can be identified: (i) photonics, which studies materials structured on a mesoscopic (micrometer or wavelength) scale, and (ii) optics of metamaterials, which are structured on a nanometer (deeply subwavelength) scales. In both these branches, revolutionary degree of control over light propagation and light-matter interaction has been achieved. However, they still remain relatively isolated fields of study.This project is aimed at developing a unified theoretical paradigm of hybrid multiscale photonics by combining the knowledge of photonics, plasmonics, and optics of metamaterials. It is expected that synergies between photonic band gap phenomena and exotic plasmonic excitations present in metamaterials will significantly enhance the possibilities for controlling the flow of light and tailoring light-matter interaction at the nanoscale.Central to the project are hybrid photonic/metamaterial systems where the elements (e.g., layers) are arranged in a periodic or aperiodic “superstructure” and themselves contain metamaterials “substructured” on a deeply subwavelength scale. The studies will start with simple geometries such as metal-dielectric multilayers with micrometer-scale superstructure and nanometer-scale substructures, moving on to more complicated 2D/3D systems based on nanowires and nanoparticle clusters.The resulting theoretical concept, applied to hybrid photonic/plasmonic/active systems (such as metal nanoparticle arrays embedded in polymer matrices doped with dye molecules), will be used to design novel plasmonic materials with low loss and/or optical gain. It will also lead to novel physical concepts such as random spasers or deterministically aperiodic photonic/plasmonic nanolasers, with applications in efficient on-chip frequency/polarization filtering, on-chip label-free sensing, and on-chip device-enhanced light-matter interactions.