Information on the environmentally dangerous properties of chemicals is of fundamental importance if the users of chemicals are to take account of the risks to the environment in their choice of chemical products, and to organize the use of chemicals and waste disposal in an environmentally safe manner. In order to assist suppliers of chemicals in setting out their product information and to ensure its consistency, it is important to have rules on classification and labelling. Such rules must be based on criteria for environmental hazard classification. During the 1980s specific classification criteria for the aquatic environment were developed in the Nordic countries and by the Commission of the European Communities. These criteria now form the basis for the regulations on classification and labelling of chemical substances in both the EC and EFTA countries. The regulations entered into force in the EC on 1 July 1992 and will be enforced in the EFTA countries as soon as possible. Besides labelling there are several other areas, e.g. transport regulations, where classification criteria are or will be applied on a national or international scale. International harmonization of criteria at this early stage is highly desirable as it will prevent the development of divergent systems which will require harmonization at a later stage. To this end, the OECD initiated a Clearing House activity on the feasibility of elaborating harmonized approaches to environmental hazard classification. The Clearing House recommended adoption of the current classification criteria, joint development of criteria for other sections of the environment and joint development of procedures for updating and methodologies for classification of chemical preparations. Further international work in this area will be coordinated by IPCS. Harmonization of classification is also a programme area under Chemical Forum with IPCS as coordinator as agreed at UNCED 92.