An injection device (110) is described having a housing (112) and a cap (130). The injection device (110) houses a syringe (114) having a needle (118) which is sealed by a boot (120). The cap (130) is arranged so that the boot (120) can be connected to the cap (130) simply, but cannot be removed from the cap (130). The housing (112) and cap (130) are arranged so that upon rotation of the cap (130), the cap (130) is moved axially away from the housing (112) and the boot (120) is removed from the syringe (114). The injection device is simple to use and manufacture.