An injection device comprising an outer housing inside which is located a medicament-holding barrel (9) with a needle (10) at one end thereof, at least part of the needle being moveable in and out of the outer housing, a plunger (8) moveable within the barrel, an inner housing (7) intermediate the outer housing (6) and the barrel and plunger and an energy source (1) in communication with said inner housing. The inner housing is moveable by the energy source between a first position in which the plunger and barrel are movable axially so as to move at least part of said needle out of the outer housing; a second position in which the plunger is movable axially into said barrel so as to expel medicament through the needle; and a third position in which the plunger and barrel are able to retract in order to retract the needle into the outer housing.