The prediction and assessment of external contamination levels around the Space Station are essential to its design, if it is to provide an acceptable space environment for the conduct of scientific experiments of long duration. Our recent study efforts on external contamination have been aimed at defining and characterizing the contamination environment around the Space Station. The objective of these studies is to assess the ability of attached payloads to function adequately in the presence of external contaminants. The studies have identified the need for detailed description of instrument degradation, especially with regard to the effect of densities of molecules and particulates that reside in the field-of-view of the instruments. At the present time, the densities and allowable limits of particle deposition are unknown. A variety of factors influence the limits, on molecular and particulate densities, including background spectral brightness and plasma processes. This paper discusses contamination analysis, in general, and the ongoing Space Station contamination studies, in particular. It identifies the contamination issues that need to be resolved and the analyses that need to be performed to provide a comprehensive picture of the Space Station contamination environment to the payload user community.