Microorganisms' natural ability to live as organized multicellular communities – also known as biofilms – provides them with unique survival advantages. For instance, biofilms are protected against environmental stresses thanks to their extracellular matrix, which could contribute to persistent infections after treatment. Biofilms are also capable of strongly attaching to surfaces, where their metabolism byproducts could lead to surface material degradation. Furthermore, microgravity can alter biofilm behavior in unexpected ways, making the presence of biofilms in space a risk for both astronauts and spaceflight hardware. Despite the efforts to eliminate microorganism contamination from spacecrafts surfaces, it is impossible to prevent human-associated bacteria or fungus from eventually establishing biofilm surface colonization. Nevertheless, by understanding the changes that biofilms undergo in microgravity, it is possible to identify key differences and pathways that could be targeted to significantly reduce biofilm formation. The Space Biofilms project, performed at the International Space Station, contributes to such understanding by characterizing the morphology and gene expression of bacterial and fungal biofilms formed in microgravity with respect to ground controls. Pseudomonas aeruginosa was used as model organism for the bacterial morphology and transcriptomic studies, while Penicillium rubens was used for the fungal morphology study. Bacterial biofilm formation was characterized at one, two, and three days of incubation (37C) over six different materials: stainless steel 316, passivated stainless steel 316, a lubricant impregnated surface (LIS), catheter grade silicone with and without a linear microtopography, and cellulose membrane.