The book examines the integration of environmental protection requirements into EU external relations focusing on unilateral, bilateral and inter-regional instruments, which have been less explored than the multilateral dimension of EU environmental policy. The book also explores for the first time the complex interplay and mutual influences between EU environmental integration initiatives and environmental multilateralism. 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 ones). On the other hand, it singles out the legal and other tools employed by the EU as a means to build partnerships with third countries in order to influence ongoing multilateral negotiations concerning the environment and sustainable development, or to contribute to the development of new international environmental norms in the absence of such multilateral negotiations. Ultimately, the book traces the significant evolution of, and complex interaction between, the various tools deployed by the EU to integrate environmental concerns in its external relations, with a view to identifying emerging challenges and future directions.