The plasmonic properties of metallodielectric nanostructures exhibit a highly sensitive dependence on geometry due to the interaction between primitive plasmon modes associated with the surfaces of the nanoparticle. Breaking symmetry increases the interactions between plasmon modes giving rise to modified, and altogether new, plasmonic features. This thesis examines the effects of breaking symmetry on three variants of a core-shell nanoparticle and a nanoparticle-nanowire plasmonic waveguide. For asymmetric core-shell nanoparticles, the far field absorption and scattering properties and the near field enhancements depend strongly on the degree of asymmetry. For nanowires, adding a vicinal nanoparticle breaks cylindrical symmetry and permits polarization-dependent coupling of visible light to propagating wire plasmons. These results offer a potential strategy for tailoring the near and far field properties of plasmonic nanoparticle systems for specific applications including high performance surface-enhanced spectroscopy, bioimaging, nanoparticle-based therapeutics, and subwavelength nanoantennae for coupling into extreme subwavelength waveguides.