A vehicle seat for supporting an occupant in a sitting position includes a backrest, and an airbag unit. The airbag unit comprises an inflatable airbag provided in an initially rolled and/or folded airbag package, and an inflator actuable to direct inflating gas into the airbag to inflate the airbag into an inflated configuration. The airbag comprises a pair of inflatable chambers which are physically connected to one another via a connecting interface, and are fluidly isolated from one another. The airbag unit is mounted and configured such that, upon actuation of said inflator to inflate the airbag, the inflatable chambers inflate into respective deployed positions in which they: i) extend forwardly from respective opposing and laterally spaced-apart side regions of said backrest; and ii) extend upwardly, and laterally inwardly across an uppermost region of the seat towards said connecting interface, so as to thereby cooperate to define an inflated shroud around at least an uppermost region of the backrest so as to extend over the sitting position and provide lateral protection to a said occupant of the seat in the sitting position.