In physics, clusters are small groups of atoms or molecules.

In science, a lot is known about properties of the gas phase; however, comparitively little is know about the condensed phases (the liquid phase and solid phase.) The study of clusters attempts to bridge this gap of knowledge by clustering atoms together and studying their characteristics. If enough atoms were clustered together, eventually one would obtain a liquid or solid.

The study of atomic and molcecular clusters also benefits the developing field of nanotechnology. If new materials are to be made out of nanoscale particles, such as nanocatalysts and quantum computers, the properties of the nanoscale particles (the clusters) must first be understood.

In addition the study of clusters has found a third phase of carbon. Diamond and graphite were previously known and in 1992 Curl, Kroto and Smalley discovered a carbon cluster consisting of 60 carbon atoms. The carbon atoms were connected to each other in the same pattern as on the traditional soccerball. They named it the Buckminster Fullerene (or Bucky ball) for which in 1996 they were awarded the Nobel prize in chemistry.