Current developments in international law witness an increase number of disputes arising out of conflicting societal values, such as the promotion of economic development versus the protection of health and the environment. Irrespective of its precise normative content, sustainable development, characterized as an "interstitial norm" or a "meta-principle", can assist in resolving these disputes in a more harmonious fashion. This chapter seeks to explore the role that sustainable development has played in the rules of the WTO. We argue that the objective of sustainable development has reshaped the interpretation of key provisions within the WTO Agreement, offering to the Members more policy space to protect essential interests. We contend that the concept has operated at the interstices of two competing priorities in WTO law: the right to free trade and economic development and the right to restrict trade in order to protect life, health, and environment.