Environmental law has traditionally set standards of individual conduct and of institutional decision-making in the exercise of rights of property and of sovereignty. These constitute liability rules by imposing liability for a breach of the rule after the event: a reactive approach. This approach continues to be relevant. It has now been complemented to a very significant extent by a proactive approach to environmental governance. This involves the acknowledgment of fundamental values and objectives – such as environmental protection, environmental restoration and sustainable development – and the creation of rules of law to implement operationally these values and objectives. These rules assume various forms: strategic rules, regulatory rules and methodological rules. Strategic rules state what is to be achieved; regulatory rules prescribe the institutional, administrative and procedural processes according to which these objectives are to be achieved; and methodological rules state the intellectual and reasoning processes according to which the decisions achieving these objectives are reached. Alternatively, there are market rules. Market rules prescribe how the market works but leave it to those operating in the market to decide how to achieve the relevant objectives but in the traditional context of contractual, tortious or statutory rules that govern how a market operates. This chapter discusses these concepts and analyses examples from international, constitutional and statutory perspectives.