Coupled plasmonic systems have been in the limelight recently for both their interesting fundamental physical properties, and their possible applications in sensing and optoelectrical system integration. Planar plasmonic systems, which can couple propagating and localized plasmons, show promise for integration of future on-chip optoelectronic devices. This thesis investigates such a system consisting of a planar metallodielectric grating coupled to spherical gold nanoparticles. It is shown that the addition of gold nanoparticles to a silver metallodielectric grating system can produce a profound change in the resonance response of the system. This coupling is shown to depend strongly on the size and surface coverage density of the gold nanoparticles.