An airbag for a vehicle occupant restraining system is provided. The airbag comprises a first inflatable area; a second inflatable area; a shoulder area arranged between the first and seconds area. The shoulder area extends in the inflated status of the airbag in the area of a shoulder and/or in an upper arm region of the vehicle occupant to be protected. The shoulder area has a thickness lower than the thickness of the first and second areas as determined in a direction vertical to the main plane of extension of the inflated airbag or comprises a recess in the airbag. The airbag is to be arranged in a vehicle such that, in case of a side collision of the vehicle, the shoulder and/or the upper arm region of the vehicle occupant strikes the shoulder area of the airbag.