A needle assembly (1, 101) for mounting on an injection device, comprising: a main body (10, 110) configured to be removably attached to an injection device in use; a needle (90, 190) secured in the main body (10, 110) and having a forward portion (92, 192) which projects forwardly from the main body (10, 110), and a shield (50, 150) including: a central portion (60, 160) which is slideably mounted within the main body (10, 110), the central portion (60, 160) including a cavity (64, 164) for at least partially receiving the needle (90, 190); and an actuator portion (70, 170) wherein the shield (50, 150) and main body (10, 110) are provided with cooperating features comprising at least one latching element having a resiliently movable leg (66, 166) provided on one of the shield (50, 150) or the main body (10, 110) and at least one corresponding engagement feature provided on the other of the shield (50, 150) and the main body (10, 110); comprising a ramped surface, for resiliently deflecting the corresponding latching element as it moves in a forward direction and a stepped or barbed profile to prevent rearward movement of the corresponding latching element when the shield (50, 150) is in a second position wherein the latching element rides over the engagement feature and snaps into a latched position as the shield (50, 150) moves into the second position to hold the shield (50, 150) in its second position. characterised in that the actuator portion (70, 170) which extends outside the main body (10, 110) is configured for pushing the shield (50, 150) forward manually in use. such that the shield (50, 150) is slideably moveable between a first position in which the forward portion of the needle (92, 192) projects forwardly of the shield cavity (64,164), and the second position in which said forward portion of the needle (92,192) is located within the shield cavity (64,164). a main body (10, 110) configured to be removably attached to an injection device in use; a needle (90, 190) secured in the main body (10, 110) and having a forward portion (92, 192) which projects forwardly from the main body (10, 110), and a shield (50, 150) including: a central portion (60, 160) which is slideably mounted within the main body (10, 110), the central portion (60, 160) including a cavity (64, 164) for at least partially receiving the needle (90, 190); and an actuator portion (70, 170) a central portion (60, 160) which is slideably mounted within the main body (10, 110), the central portion (60, 160) including a cavity (64, 164) for at least partially receiving the needle (90, 190); and an actuator portion (70, 170) wherein the shield (50, 150) and main body (10, 110) are provided with cooperating features comprising at least one latching element having a resiliently movable leg (66, 166) provided on one of the shield (50, 150) or the main body (10, 110) and at least one corresponding engagement feature provided on the other of the shield (50, 150) and the main body (10, 110); comprising a ramped surface, for resiliently deflecting the corresponding latching element as it moves in a forward direction and a stepped or barbed profile to prevent rearward movement of the corresponding latching element when the shield (50, 150) is in a second position wherein the latching element rides over the engagement feature and snaps into a latched position as the shield (50, 150) moves into the second position to hold the shield (50, 150) in its second position. characterised in that at least one latching element having a resiliently movable leg (66, 166) provided on one of the shield (50, 150) or the main body (10, 110) and at least one corresponding engagement feature provided on the other of the shield (50, 150) and the main body (10, 110); comprising a ramped surface, for resiliently deflecting the corresponding latching element as it moves in a forward direction and a stepped or barbed profile to prevent rearward movement of the corresponding latching element when the shield (50, 150) is in a second position wherein the latching element rides over the engagement feature and snaps into a latched position as the shield (50, 150) moves into the second position to hold the shield (50, 150) in its second position. characterised in that the actuator portion (70, 170) which extends outside the main body (10, 110) is configured for pushing the shield (50, 150) forward manually in use. such that the shield (50, 150) is slideably moveable between a first position in which the forward portion of the needle (92, 192) projects forwardly of the shield cavity (64,164), and the second position in which said forward portion of the needle (92,192) is located within the shield cavity (64,164).