Clusters, comprised of an assembly of atoms or molecules, sometimes attached to ions, constitute a form of matter in which the individual constituents are aggregated together by forces that are relatively weak compared to those responsible for chemical bonding. Hence, the ter minology is usually reserved to describe systems whose bonding is conveniently discussed as van der Waals-like, thereby involving weak dispersion forces, but it also describes systems where electrostatic forces, hydrogen bonding, and even metal-metal bonding may be operative. The term "clusters" is used to describe collections of molecules on a surface, complexes existing in the condensed phase, large inorganic and organo metallic complexes, as well as isolated assemblies existing in the gas phase. With such a broad definition, it is not surprising that the literature devoted to the subject is enormous and pervades a wide range of fields involving both science and technology. Reference to potential applications of research on clusters includes literature devoted to materials processing, photography, microelectronics, catalysis, atmospheric and interstellar chemistry, and even the fueling for fusion reactors, to name a few examples. Perhaps the overriding reason for the extensive activity in the field derives from the promise that studies of such systems will serve to bridge the gap between an understanding of isolated atomic and molecular systems, on the one hand, and a microscopic understanding of condensed matter on the other. In this regard, work on systems of increasingly higher degrees of aggregation serve to elucidate the molecular details of the collective effects responsible for phase transformation (nucleation phe nomena), the development of surfaces, and solvation. In other areas,