This chapter discusses the surface analysis of small individual particles through the use of secondary ion mass spectroscopy (SIMS). Two different designs of SIMS instruments, the ion microscope and the ion microprobe, are available for the bulk and surface analyses of single small particles. Through the advancement and refinement of SIMS techniques it is now possible to analyze both the surface and the bulk properties of individual small particles, with good spatial resolution and high sensitivity. In spite of numerous limitations, SIMS is a very viable analytical technique for determining the surface chemical composition of particles down to the submicrometer size range. Surface analyses of solids by secondary ion mass spectrometry are usually performed on samples that, for practical purposes, are infinite. That is, the ratio of the sample area to area of the primary ion beam is very large.