The background to the passage of the seat belt usage law in Britain is described. Voluntary belt use rates in the 1970's were approximately 30%, with educational campaigns having a minimal effect. The political process and the factors influencing the seat belt legislation are described, particularly the role of the media. The provisions and the consequences of the law are outlined with belt use in the general traffic stream rising to 90%. Deaths and serious injury to front seat car occupant casualties declined by 25% in comparing the year after with the year before the introduction of the law. Changes in other categories of casualties were within normal statistical limits and were uninfluenced by the seat belt legislation.