Publisher Summary This chapter provides an overview of the origins and development of the public information requirement concerning major accident hazards. The chapter describes the main features of the debate concerning major accident hazards and discusses the precedents to the “Seveso Directive.” The seriousness of the accident became known only by stages, as there were delays from the part of the company to release the full information. This lack of information created delays in the emergency response. The local authorities had to figure out what had actually happened and what needed to be done on the basis of partial and unreliable information. The analyses of the accidents that encouraged the regulatory process showed that the lack of prior information, on both the risks and the appropriate safety measures to be adopted, was one of the major failures in providing adequate safety to the workers, the population, and the environment. A central piece of the legislation is the requirement for public information about risks, safety measures, and appropriate behavior to take in the event of an accident. Thus, the “Seveso I Directive” first enshrined the need or right to know principle for the general public. Prior to it, the principle was recognized only for workers in specific manufactures and/or working processes.