Crew members flying llong duration spaceflight missions report highly individualized responses in their ability to remember tasks and to recall information. Operations aboard Space Station Mir demonstrated that over the course of a mission, toxic exposures were possible during contigencies. This clearly indicated the need for some form of objective cognitive assessment to ensure crew safety. The Spaceflight Cognitive Assessment Tool (S-CAT) was created under the guidance of the NASA Johnson Space Center’s Behavioral Health and Performance program. The purpose of the S-CAT is to provide an objective measure of cognitive function for crew members and their flight surgeons during space missions. This paper describes the development and the components of the S-CAT.