This paper describes the background and contents of European Union legislation in the area of prevention of major accidents in fixed industrial installations, especially the famous ＇Seveso Directive＇. The legal basis, aims and obligations of both the old ＇Seveso I Directive＇ (82/501/EEC) and the new ＇Seveso II Directive＇ (96/82/EC) are explained in detail with regard to their prescriptions on accident prevention.