Biodeterioration of polymeric materials affects a wide range of industries. Formation of microbial biofilms on surfaces of materials being considered for use on the International Space Station was investigated. The materials included fiber-reinforced polymeric composites, adhesive sealant, polyimide insulation foam, Teflon cable insulation, and aliphatic polyurethane coatings. In simulation experiments, bacterial biofilms formed readily on the surfaces of the materials at a wide range of temperatures and relative humidity. The biofilm population was dominated by Pseudomonas aeruginosa, Ochrobactrum anthropi, Alcaligenes denitrificans, Xanthomonas maltophila, and Vibrio harveyi. Subsequently, degradation of polymeric materials was mostly a result of both fungal and bacterial colonization in sequence, and fungi may have advantages in the early phase of surface colonization over bacteria, especially on relatively resistant polymeric materials. These microorganisms are commonly detected on spacecraft on hardware and in the air. Furthermore, degradation of polymeric materials was documented with electrochemical impedance spectroscopy (EIS). The mechanisms of deterioration of polymeric materials were due to the availability of carbon source from the polymer, such as additives, plasticizers, and other impurities, in addition to the polymeric matrices. Microbial degradation of plasticizer phthalate esters is discussed for the microorganisms involved and the biochemical pathways of degradation. Current results suggest that candidate materials for use in space missions need to be carefully evaluated for their susceptibility to microbial biofilm formation and biodegradation.