Beyond classical electrodynamics : mesoscale electron dynamics and nonlinear effects in hybrid nanostructured systems This work investigates the optial properties of hybrid metal dielectric and ionic solid largely regular nanostructures in the presence of nanosized features such as gaps and thin walls in tubular structures. The fundamental optical response of plasmonic ionic and dielectric systems is considered from a classical electromagnetic perspective including properties of amorphous materials rough interfaces nonlinear and semi classical charge interactions. We focus hereby on two aspects: (i) nonclassical effects stemming from the quantum nature of freely moving charges and (ii) nonlinear optical response. The overall aim is to realistically describe complex nanoparticle distributions and ultrathin multilayers with reliable and rapid methods of computational nanophotonics while extending its scope towards multiphysics aspects beyond classical electrodynamics. The analytical and numerical models developed over the past years are presented in this work in detail with standard but necessary technical details available in the appendices. We often assume a multilayered system where one layer is a nanostructure with either one or two dimensional symmetry i.e. a grating or laminar structure in the first and an array of nanoparticles (disks holes pillars etc.) in the latter case. Given the symmetries and overall composition of the structure our method of choice is the Fourier Modal Method (FMM) together with the scattering matrix approach to connect the different layers. The standard FMM formulation is extended to include spatial dispersion effects of conduction band electrons in metals introducing not only an additional boundary condition but an overall third longitudinal solution to the standard transversal solutions of the electromagnetic wave equation. Furthermore we explore the impact of higher harmonic waves in particular second and third harmonic generation from the local fields around the nanostructures studied.