This book examines the little-explored unilateral, bilateral, and inter-regional dimensions of EU external environmental policy, in light of the Treaty-based requirement of environmental integration, both at the formulation and at the implementation stages. The book thus explores the interplay between these dimensions of the EU's external environmental activities and international environmental law from a dual perspective. On the one hand, it identifies the legal and other instruments used by the EU to support the implementation of multilateral environmental agreements in third countries (particularly, developing countries). And, on the other hand, it singles out the legal tools employed by the EU to build partnerships with third countries as part of the process of influencing multilateral negotiations on the environment and sustainable development. Ultimately, the book traces the evolution of, and the complex interaction between, the multiple legal tools deployed by the EU to integrate environmental concerns in its external relations, with a view to identifying emerging challenges and future directions. (Series: Modern Studies in European Law - Vol. 29)