Regulatory toxicology is the process whereby information relevant to the evaluation of the toxicity of agents is obtained by organizations and evaluated by or on behalf of governmental or international organizations. The aim is to protect workers, consumers, the public generally and the environment. The requirements of many regulatory systems are closely defined in terms of both the studies required and the interpretations to be placed upon the results obtained. There are various models for the regulation of chemicals, which may be based upon equity, utility or technical feasibility criteria, or a combination of these. Some chemicals are subject to premarketing authorization systems, so that the organization which wishes to market the substance needs permission before doing so. In most countries, the marketing of human and veterinary pharmaceuticals follows this pattern. Other systems have lists of allowed or proscribed substances or are simply notification schemes. With the latter, the individual substance does not need to be authorized but its use/sale/manufacture has to notified, together with the basic properties of the compound. There has been a recent trend to harmonize regulatory systems within trading blocks such as the European Union (EU) and North American Free Trade Area (NAFTA) and also between these blocks.