A casing (50) for an injection device (10) of the type having a safety device which prevents operation of the device (10), incorporating an actuator means (56) by which the safety means of the device (10) can be actuated to allow operation of the device (10). Also a casing (50) for a medicament container having an opening closed prior to use by a break-off tip (135), having relatively moveable first and second casing parts (51, 52), which on relative movement apply a breaking force to the break-off tip (135). A preferred embodiment includes both such features.