Gold nanoparticle arrays exhibit extraordinary spectral properties useful to a wide variety of applications including biomolecular sensing, alternative energy, and informatics. The spectral properties of these arrays depend on the array geometry (particle size and spacing) and the surrounding environment (refractive index). In this thesis, a thorough map of the parameter space describing the spectral properties of square, gold nanoparticle arrays is developed in conjunction with a fundamental theoretical description of the phenomena that govern these properties