The precautionary principle is certainly one of the most fundamental of international environmental law. Symbolic of a "technical democracy", this principle has been one of the cornerstones of the Rio Declaration. Its proclamation was then the starting point of a broad and rapid development of the principle –or the approach– of precaution which today underlies many legal systems. Little by little, international courts have, by a constructive dialogue, gradually highlighted the precautionary principle, whether its authority or its contents and its implications. Its complex and composite nature continues to be a challenge. But in nowadays societies, characterized by a constant technical innovation, its introduction in positive law seems quite irresistible. Judges are expected to play an important role in the development of this "open textured" standard. In such a context, the dialogue –or at least the benevolence– between judges including between international, European and domestic judges, may still be helpful, and could contribute to feed and stabilize the case-law.