Metal-dielectric nanostructures capable of supporting electromagnetic resonances at optical frequencies are the vital component of the emerging technology called plasmonics. Plasmon is the electromagnetic wave confined at the metal-dielectric interface, which may effectively couple to the external electromagnetic excitation with the wavelength much larger than the geometric size of the supporting structure. Plasmonics can improve virtually any electromagnetic technology by providing subwavelength waveguides, field enhancing and concentrating structures, and nanometer size wavelength-selective components. The focus of this work is the fabrication, characterization and modeling for novel plasmonic nanostructures. Effects of the symmetry in plasmonic structures are studied. Symmetric metal nanoparticle clusters have been investigated and show highly tunable plasmon resonances with high sensitivity to the dielectric environment. Efficient, highly-scalable methods for nanoparticle self-assembly and controlled partial submicron metal sphere coatings are developed. These partially Au coated dielectric spheres have shown striking properties such as high tunability, as well as the control on resonant electromagnetic field enhancement and scattering direction. Studied effects are of vital importance for plasmonics applications, which may improve virtually any existing electromagnetic technology. Optical resonances in metal-dielectric nanostructures were correlated with LC circuit resonances elaborating on the resonance tunability, dielectric environment, symmetry breaking and mode coupling (Fano resonance) effects.