The European Agreement concerning the International Carriage of Dangerous Goods by Road, commonly known as ADR (from the French abbreviation Accord européen relatif au transport international des marchandises Dangereuses par Route), governs transnational transport of hazardous materials.

Launched in Geneva on 30 September 1957 under the aegis of the United Nations' Economic Commission for Europe, it first took effect on 29 January 1968. The agreement was modified (article 14, paragraph 3) in New York on 21 August 1975, though these changes only took effect on 19 April 1985. A new amended ADR 2012 entered into force on 1 January 2012

The agreement itself is brief and simple, and its most important article is article 2. This article states that with the exception of certain exceptionally dangerous materials, hazardous materials may in general be transported internationally in wheeled vehicles, provided that two sets of conditions be met:

1.Annex A regulates the merchandise involved, notably their packaging and labels.
2.Annex B regulates the construction, equipment and use of vehicles for the transport of hazardous materials.

The classes of dangerous goods according to ADR are the following:

Class 1: Explosives
Class 2: Gases
Class 3: Flammable liquids
Class 4: Flammable solids
Class 5: Oxidizing agents and organic peroxides
Class 6: Toxic and Infectious Substances
Class 7: Radioactive substances
Class 8: Corrosive substances
Class 9: Miscellaneous

Reference: WHO (updated June 2017)