Contamination associated with ion implantation is reviewed with an emphasis on secondary ion mass spectrometry (SIMS) characterization. Specific examples are provided using SIMS as a tool to detect and resolve contaminant problems. This study of contamination is organized according to the path of the ion beam through an ion implanter, starting with the source and continuing to the end station. The source material, ion source components, and vacuum system can produce contaminant mass interferences that may not be eliminated by mass filtration in the implanter. A table of possible mass interferences is provided. The mass resolution of the implanter may be insufficient to remove adjacent masses and therefore may permit additional contaminants in the mass-analyzed ion beam. Charge exchange and molecular ion dissociation due to poor vacuum can occur at several locations in the implanter, especially after mass separation but before final acceleration. Detailed examples of BF2 dissociation are presented. Collisions of the ion beam with end station components result in low energy deposition of contaminants that can be driven into the target by the ion implanting beam. The fluence of the species of interest can be in error. Examples of multiple contaminant sources are also provided.