This article examines the emergence of green sukuk as an instrument situated at the intersection of Islamic finance, sustainable finance, and comparative financial regulation, with particular reference to the Organization of Islamic Cooperation (OIC) and the European Union (EU). The study argues that green sukuk may represent a distinctive mechanism for financing sustainable development because they combine Sharia-compliant financial structures with environmental, social, and governance (ESG) objectives, thereby linking ethical finance to climate-transition strategies. After outlining the legal and operational characteristics of sukuk and their evolution within Islamic finance doctrine and AAOIFI standards, the article analyses the increasing role of green sukuk in financing renewable energy, climate adaptation, and sustainable infrastructure projects across OIC jurisdictions, particularly in Malaysia, Indonesia, Saudi Arabia, and the Gulf region. The article then explores the European dimension of sustainable Islamic finance through the lens of the European Green Deal, the EU Taxonomy Regulation, and the “Do No Significant Harm” principle, underscoring convergences and tensions between EU sustainability regulation and Sharia governance. Adopting a comparative-law methodology, the article highlights how green sukuk serves as a privileged vantage point for analyzing the broader transformation of contemporary financial law into a plural and transnational normative space. Finally, the article analyses the central role of the doctrinal formant in shaping Islamic financial law, focusing on AAOIFI Sharia Standard No. 62 and the transition from asset-based to asset-backed sukuk structures. It is argued that the future credibility of green sukuk markets depends upon the development of transnational governance mechanisms capable of preventing both greenwashing and “Sharia-washing” through stronger disclosure, environmental oversight, and interdisciplinary expertise. The article concludes that green sukuk may constitute an important component of global sustainable finance, provided that regulatory harmonization, secondary-market development, and integrated Sharia-environmental governance continue to evolve within an increasingly transnational legal framework.