An injection system comprising: an injection device, the injection device comprising: a replaceable syringe comprising a fluid container and a discharge nozzle; a housing adapted to receive the syringe which is movable between a retracted position in which the syringe is wholly contained in the housing and an extended position in which at least part of the discharge nozzle extends out of the proximal end of the housing; a drive; an actuator mechanism connected to the drive, the actuator mechanism having an unactuated state in which it does not act on the drive and an actuated state in which it has acted on the drive and moved the syringe to its extended position and expelled the contents of the fluid container; and a trigger mechanism which is operable to cause the actuator mechanism to move from its unactuated state to its actuated state and thereby move the syringe to its extended position and expel the contents of the fluid container; and a base station; wherein the injection device and the base station are adapted such that the base station connects to the distal end of the housing of the injection device and resets the actuator mechanism from its actuated state to its unactuated state so that further actuation of the actuator mechanism can take place. an injection device, the injection device comprising: a replaceable syringe comprising a fluid container and a discharge nozzle; a housing adapted to receive the syringe which is movable between a retracted position in which the syringe is wholly contained in the housing and an extended position in which at least part of the discharge nozzle extends out of the proximal end of the housing; a drive; an actuator mechanism connected to the drive, the actuator mechanism having an unactuated state in which it does not act on the drive and an actuated state in which it has acted on the drive and moved the syringe to its extended position and expelled the contents of the fluid container; and a trigger mechanism which is operable to cause the actuator mechanism to move from its unactuated state to its actuated state and thereby move the syringe to its extended position and expel the contents of the fluid container; and a replaceable syringe comprising a fluid container and a discharge nozzle; a housing adapted to receive the syringe which is movable between a retracted position in which the syringe is wholly contained in the housing and an extended position in which at least part of the discharge nozzle extends out of the proximal end of the housing; a drive; an actuator mechanism connected to the drive, the actuator mechanism having an unactuated state in which it does not act on the drive and an actuated state in which it has acted on the drive and moved the syringe to its extended position and expelled the contents of the fluid container; and a trigger mechanism which is operable to cause the actuator mechanism to move from its unactuated state to its actuated state and thereby move the syringe to its extended position and expel the contents of the fluid container; and a base station; wherein the injection device and the base station are adapted such that the base station connects to the distal end of the housing of the injection device and resets the actuator mechanism from its actuated state to its unactuated state so that further actuation of the actuator mechanism can take place.