Ionized cluster beams (ICB) are widely used to deposit metal, semiconductor and insulating films. This paper describes the current state of this technology in both fundamental and applications areas. ICB provides tight control of the kinetic energy and ion content of the beam, which gives the technique a unique advantage compared to MBE, VPE, LPE, MOCVD, sputtering or other thin film deposition methods. The development of this technology should allow the deposition of high quality material at low temperature onto a wide variety of substrate surfaces and even permit the formation of thin film materials not previously possible.