The unique development environment of NASA's Space Station Freedom (SSF) creates numerous challenges to the design of a common user interface for operating the spacecraft. Astronauts on board SSF will utilize multi-purpose workstations as their primary command and control interface to the vehicle. With the exception of some dedicated hardware controls, the vast majority of the workstation user interface will be implemented in software. The specification and design of the SSF user interface requires the synthesis of on-orbit operational requirements with multiple systems' functional requirements, all of which emanate from geographically and organizationally distributed entities. Human factors requirements as well as constraints imposed by the SSF Displays and Controls (D&C) system architecture are additional considerations. User interface technology has reached a state of maturity, and SSF user interface integration activities are ensuring that existing technology is maximally applied to the design of SSF. Diverse requirements for operating this manned spacecraft are being brought into harmony via the user interface integration process.