This chapter discusses the uplink process. Demands for reliability on both ground and platform portions of the uplink process have increased. More stringent requirements for error-free commanding, flexibility in on-board execution of commands, automated checking for both invalid commands and for adherence to overall mission rules regarding safety and longevity, and cost-efficient payload operations have served to increase the complexity of uplink systems. Design of the mission planning task must take into account the mission’s requirement to accept late changes. A useful solution to all of the problems is to design the command system to treat these variables as parameters in commands that can otherwise be constructed early. A flight software function continually checks the time-tag on the next sequential command against the current on-board clock time and issues the command to the designated subsystem or instrument when the time is reached.