Secondary ion mass spectrometry (SIMS) is a widely used technique for the determination of both the surface and in-depth elemental and molecular composition of a wide variety of solid materials. The National Institute of Standards and Technology has been at the forefront of SIMS research for nearly 30 years. A major recent activity at NIST has been the development and application of Cluster SIMS. In SIMS, the surface to be analyzed is bombarded in ultrahigh vacuum with an energetic ion beam (typically Ar@super +@, O@sub 2@@super +@, Cs@super +@ or Ga@super +@) with subsequent detection of characteristic sputtered secondary ions by mass spectrometry. In the Cluster SIMS approach, the standard ion beams are replaced with small polyatomic or cluster primary ions such as SF@sub 5@@super +@ or C@sub 10@@super -@. When a cluster ion strikes a surface with several keV of energy, it dissociates into its constituent atoms with each constituent retaining a fraction of the initial energy. The reduction in impact energy results in a reduced penetration depth below the surface and the possibility for improved SIMS depth resolution. The dissociation of the cluster ion also leads to a localized deposition of energy in the near-surface region of the sample that may enhance the yield of characteristic molecular ions by several orders of magnitude providing greater sensitivity for organic surface characterization. Research at NIST in Cluster SIMS covers the range from ion source development to demonstration of Cluster SIMS advantages in applications to semiconductors, polymers, and biomolecules.