EDOARDOCROCI IEFE - Università Bocconi, Milano, Italy Voluntary approaches in environmental policy represent a “third wave” of regulation in the environmental field. “Command and control” was the first wave. Its core is based on uniform emission standards, the respect of which needs to be enforced through extensive monitoring and severe sanctions. The expected cost of sanction for non-compliance, calculated as its amount multiplied for the probability to be caught, must be superior to the benefits of non-compliance, in order to let the sanction be effective. As the benefits of non-compliance can vary among firms, sanctions need to be very high in order to be effective. In fact sanctions are ordinary correlated to environmental damage and not to the benefits of non-compliance. But very high sanctions can be difficult to enforce as they appear unfair and can lead to dramatic consequences on firms and workers, up to shut-downs of plants. Ambient standards reduce these problems, but oblige the regulator to know a huge amount of information, regarding the specific contribution of each polluter to the polluted body. Information is difficult to obtain because of asymmetric information and costly to produce because it requires large and skilled regulating and enforcing organizations. Nevertheless complex regulation is the base of any environmental policy framework, as it allows the policy maker to fully exercise its power of composition of various interests in a relatively transparent way. Economic instruments were the second wave.