Metallic nanoparticles show a rich optical behaviour because of their strong light absorption and scattering, wide spectral tunability, and interesting optical near-field effects. Research into optical effects of metallic nanoparticles, a field with a long tradition, has been developing rapidly in recent years as a result of progress in nanoparticle fabrication, spectroscopic techniques, and computational methods. This article provides a survey of optical effects of metallic nanoparticles, covering both fundamental phenomena and emerging applications.