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The manipulation of light at the nanoscale has become a fascinating research field called nanophotonics. It brings together a wide range of topics such as semiconductor quantum dots or molecular optoelectronics and the study of metal optics, or plasmonics, on one hand and the development of finely designed structures with specifically engineered optical properties called metamaterials on the other. As is often the case, it is at the boundary of these two domains that most novel effects can be observed. Plasmonics has for instance enabled the detection of single molecules due to the large field enhancement which exists in the vicinity of nanostructured metals. Thanks to the confinement of electromagnetic waves below the diffraction limit plasmonic systems are also foreseen as ideal conduits connecting electronic and photonic systems. On another hand, when a material is patterned on a scale smaller than the wavelength, its optical properties are reflections of the structure of the patterned material rather than the material itself, a concept known as metamaterial. This has allowed researchers to obtain exotic optical properties such as negative refractive indices and can be implemented in devices acting like invisibility cloaks or perfect lenses. While the prospects for nanophotonics are far-reaching, real-life applications are severely limited by the intrinsic absorption of metals and the current fabrication methods mostly based on electron-beam lithography which is slow and costly. In this thesis, we investigate these issues by considering the potentials of other polaritonic materials such as semiconductors, silicon carbide and graphene for field confinement applications. This is achieved through the combination of both numerical studies and sample fabrication and testing with the help of international collaborators. Our results show much improvement over the metallic structures typically used, with an operating range covering the near- and mid-infrared as well as the terahertz. The field compression can also be much greater compared to conventional plasmonic materials, with near-field enhancements reaching four orders of magnitude. Furthermore, we analyse theoretically the optical properties of metallic gyroids which are obtained by self-assembly - a promising chemical route for fabricating large-scale 3D structures with molecular sized resolution. These materials exhibit unexpected properties such as negative refraction and could in consequence be used as thin lenses or wave-plates. Last, we develop and apply a theoretical formulation of Fano theory for the case of plasmonics. It allows a clear and simple physical understanding of the interference spectra which are commonly encountered in nanooptics. Open Access