The precaution principle that is often referred to in the field of environment and public health, imposes to take the measures required to avoid the risk of serious and irreversible damage, even when this risk is not certain – which distinguishes it from the prevention principle. Today this principle is consecrated in numerous international conventions ; doubtlessly hastily, some even confer it a customary value. Nevertheless, it remains difficult to agree on its precise (juridical) content. Contrary to prevention, the precaution duty has no incidence on the juridical regime of damage repair ; what it commands is rather the preparation of the conditions in which the public – « political » – decision is taken, in a society due to determine democratically the socially acceptable risks. In the immediate future, the risk is that the precaution principle should serve first of all the particular interests of the mightiest, which could discredit it to the eyes of the greater number. – Summary AFRI-2002