The present state of understanding of vibrational properties of self-interstitial atoms (SIAs) in metals is reviewed. The thoery of vibrations of SIAs in metals is discussed. The vibrational behaviour of <100>-dumbbell in fee metals and <110>-dumbbell in bcc metals is treated in detail with the use of Green's function method showing the occurrence of resonance modes and localized modes of SIAs. Changes of various physical properties due to SIAs—the thermodynamic properties including a critical examination of different methods of evaluation of formation entropy, diffuse inelastic scattering of neutrons, dispersion curve, and elastic constants—are discussed. The vibrations of multiple interstitials are also discussed. The vibration of SIAs in hep metals is briefly reviewed. The need for and direction of further work is indicated.