The iron and steel industry generates considerable tonnages of solid waste, and although much of it is to a large extent valorized, some 50 kg of waste to every tonne (1000 kg) of steel have to be discharged or disposed of as waste. A good environmental protection policy calls for a ban on dumping of special waste materials, which there are strong grounds for fearing may be of a toxic and dangerous nature. Except in specific cases, it is difficult to tell from the composition of a waste material whether or not it is of a “special” nature. Characterization simulations have to be made to ascertain the extent to which the waste material can release harmful elements, such as heavy metals, when in contact with rainwater and in some cases other waste materials. Such is the object of the leaching tests, which have or are being developed in many countries at the instigation of the authorities and industrialists: Federal Republic of Germany, South Africa, Australia, France, Great Britain, Italy, Japan, the United States, and so forth. The International Iron and Steel Institute (IISI) has, within its Environment Committee, made a comparison of the results obtained with different national tests using the same specimens.