This book looks into areas in which the relationship between environmental policy and trade policy at the international level is unresolved and subject to debates and negotiations. Most controversial is the treatment of standards on processes and production methods (PPMs) when a product is traded. Should the way a product is manufactured or the resources being exploited in this process be considered when allowing market access - although the product itself does not exhibit these information? According to the principles and rules of the World Trade Organization the answer is "yes." Exemptions, yet possible, are not clearly defined and need case-by-case legal judgements in order to become more applicable. This book argues that international environmental agreements deliver the necessary background for environmentally motivated trade measures but still lack the legal power to be considered ex ante. The only viable policy instrument that helps to make the hidden environmental effects of traded goods more transparent are labels and certificates. Thus, the book focuses on three aspects: First, how do the multilateral environmental agreements which explicitly include trade measures relate to WTO rules? Second, could the integration of negotiations in the two policy fields induce a more efficient outcome with respect to trade rules and to environmental protection? And third, could ecological labels deliver a solution to potential trade rule conflicts inherent to different national treatment of so-called like products which differ in their production processes?