An air bag assembly.for cushioning restraint of an occupant in a vehicle during an impact event, the air bag assembly comprising: an inflator activatable to discharge inflation gas upon the occurrence of predetermined vehicle conditions; an air bag cushion in fluid communication with the inflator such that upon discharge of inflation gas from the inflator the air bag cushion is inflated to a deployed state from a location of deployment in substantially opposing relation to the occupant; a tether (30, 35) comprising at least one profile restraining tether element, the tether (30, 35) extending from the air bag cushion and being adapted to attach to a releasable anchor structure (37, 48) so as to shorten the operative length of the tether (30, 35); and an actuation mechanism activatable based upon measurements from one or more sensors (22, 24, 26, 27) measuring conditions of the occupant during activation of the inflator, the actuation mechanism being adapted to release the tether (30, 35) from the releasable anchor structure (37, 48) upon the occurance of predetermined occupant conditions thereby extending the operative profile of the air bag cushion; characterised in that the air bag assembly further comprises an actuatable variable inflation device to control the amount of inflation gas discharged into the air bag cushion, wherein the actuatable variable inflation device comprises a vent blocking member alignable with a vent opening within a housing in which the inflator is disposed, the vent blocking member being moveable relative to the vent opening upon activation of the actuation mechanism thereby adjusting the effective venting area of the vent opening. an inflator activatable to discharge inflation gas upon the occurrence of predetermined vehicle conditions; an air bag cushion in fluid communication with the inflator such that upon discharge of inflation gas from the inflator the air bag cushion is inflated to a deployed state from a location of deployment in substantially opposing relation to the occupant; a tether (30, 35) comprising at least one profile restraining tether element, the tether (30, 35) extending from the air bag cushion and being adapted to attach to a releasable anchor structure (37, 48) so as to shorten the operative length of the tether (30, 35); and an actuation mechanism activatable based upon measurements from one or more sensors (22, 24, 26, 27) measuring conditions of the occupant during activation of the inflator, the actuation mechanism being adapted to release the tether (30, 35) from the releasable anchor structure (37, 48) upon the occurance of predetermined occupant conditions thereby extending the operative profile of the air bag cushion; characterised in that the air bag assembly further comprises an actuatable variable inflation device to control the amount of inflation gas discharged into the air bag cushion, wherein the actuatable variable inflation device comprises a vent blocking member alignable with a vent opening within a housing in which the inflator is disposed, the vent blocking member being moveable relative to the vent opening upon activation of the actuation mechanism thereby adjusting the effective venting area of the vent opening.