Why is it useful to compare Islamic environmental law to environmental common law? This chapter explores on one hand the similarities between Islamic law and common law both in general and in the field of environmental law. On the other hand, it analyzes the divergences between these two legal systems. The first section of the chapter focuses on the idea that if the Trust is at the heart of the common law, it is also at the heart of Islamic law. The second section explains how the Trust has evolved in the framework of the common law and contrasts it with the evolution of Waqf in Islamic law. The purpose of this comparison is to help find new avenues for the evolution of Islamic environmental law. As the common law has succeeded in evolving Trusts in the field of environmental law, so canIslamic law. The few Muslim countries which are using the Waqf for environmental purposes today are mostly mixed Sharia’/common law countries or are at least former British colonies. Muslim countries not using the environmental potential of the Waqf are in general Sharia’/civil law countries. This could be explained by the facility with which the Waqf can evolve in a common law context because of its numerous synergies with the Trust.