An auto-injection apparatus for receiving a syringe, the apparatus comprising: an outer casing which encloses a drive assembly having a delivery spring for driving a plunger into a barrel of the syringe which contains a substance for injection, a syringe carrier configured to hold the barrel of the syringe, the syringe carrier being forward of the drive assembly and not extending beyond a distal end of the barrel and having a stowed position and a delivery position, an insertion spring for inserting a needle of the syringe into an injection site, the insertion spring being located at a distal end of the outer casing and acting on the drive assembly, an interlock forward of the distal end of the syringe carrier and which extends between the syringe carrier and a syringe carrier housing which at least partially surrounds the syringe carrier, the interlock preventing the forward motion of the syringe carrier under the influence of the insertion spring whilst in the stowed position, the insertion spring being arranged prior to release of the interlock to urge the syringe carrier forwards, relative to the outer casing via the abutment between the drive assembly and syringe carrier, which abutment is via the barrel and to drive the drive assembly and the syringe carrier forward once the interlock has been released, a shield which is arranged to shroud the needle at least prior to an injection and which is slidably arranged between the outer casing and the syringe carrier, and an interlock release mechanism which is configured to release the interlock and wherein the interlock release mechanism comprises said shield which provides a pressure activated trigger for the interlock release mechanism. a drive assembly having a delivery spring for driving a plunger into a barrel of the syringe which contains a substance for injection, a syringe carrier configured to hold the barrel of the syringe, the syringe carrier being forward of the drive assembly and not extending beyond a distal end of the barrel and having a stowed position and a delivery position, an insertion spring for inserting a needle of the syringe into an injection site, the insertion spring being located at a distal end of the outer casing and acting on the drive assembly, an interlock forward of the distal end of the syringe carrier and which extends between the syringe carrier and a syringe carrier housing which at least partially surrounds the syringe carrier, the interlock preventing the forward motion of the syringe carrier under the influence of the insertion spring whilst in the stowed position, the insertion spring being arranged prior to release of the interlock to urge the syringe carrier forwards, relative to the outer casing via the abutment between the drive assembly and syringe carrier, which abutment is via the barrel and to drive the drive assembly and the syringe carrier forward once the interlock has been released, a shield which is arranged to shroud the needle at least prior to an injection and which is slidably arranged between the outer casing and the syringe carrier, and an interlock release mechanism which is configured to release the interlock and wherein the interlock release mechanism comprises said shield which provides a pressure activated trigger for the interlock release mechanism.