The plasmon resonance in small metal particles and structures is extremely sensitive to both the size and the shape of the particle. This feature enables materials to be developed with tunable optical resonances throughout the visible and nearinfrared spectral region through changes to the particle morphology. However, chemical synthesis invariably yields a range of particle sizes and frequently different shapes. Thus, the extinction spectra or scattered-light spectra obtained in these cases are statistical averages over all particle sizes and shapes present within the ensemble. This has rendered the determination of the size and shape dependence of surfaceplasmon modes a difficult problem.