The Environmental Defense Fund (EDF) is a leading United States-based nonprofit environmental advocacy organization founded in 1967. It originated from a group of scientists, citizens, and lawyers on Long Island, New York, who successfully challenged the use of the pesticide DDT through a class action lawsuit against the Suffolk County Mosquito Control Commission, marking the first such environmental legal action in the U.S. This victory led to the formal incorporation of EDF, which has since grown into a global entity focused on addressing environmental challenges through the integration of science, economics, and law. EDF emphasizes practical, market-based solutions and nonpartisan approaches to issues such as global warming, ecosystem restoration, ocean conservation, human health protection, and innovation in clean energy and sustainability.

The organization collaborates with businesses, governments, and other stakeholders to implement innovative strategies, including corporate partnerships and policy advocacy. Headquartered in New York City, EDF operates worldwide with over 1,000 staff members, including scientists, economists, lawyers, and policy experts, and boasts more than 3.5 million members and activists. It has been instrumental in landmark achievements, such as the U.S. ban on DDT, influencing the Paris Agreement, developing cap-and-trade programs like California's, and pioneering market-based environmental solutions through economic incentives and partnerships with companies like McDonald's and Walmart to reduce waste and emissions. EDF has been involved in significant legal actions, litigation, policy advocacy, and research initiatives leading to environmental protections including air and water pollution reduction, sustainable fisheries management, and climate change mitigation.

EDF maintains a strong financial position, with annual revenues exceeding $200 million primarily from contributions and grants, and is highly rated by evaluators like Charity Navigator for its efficiency and impact. The organization receives funding from diverse sources including foundations, individuals, and corporate partners, and is known for transparency in operations and impact reporting. EDF's work extends to international consultations, including with governments in China and Mexico, and affiliations with bodies like the International Union for Conservation of Nature. While nonpartisan, it actively lobbies U.S. Congress and engages in litigation, having sued entities like the Environmental Protection Agency and the American Chemistry Council.

Despite its collaborative ethos, EDF has faced criticism from more traditional environmental groups like the Sierra Club for its business partnerships, which some view as compromising advocacy, with some critics accusing EDF of being too conciliatory toward industry, particularly regarding partnerships on cap-and-trade systems. The organization defends its pragmatic approach as essential for achieving real-world progress. EDF continues to expand its influence through educational outreach, public campaigns, and international collaborations aimed at stabilizing the climate, fostering healthy communities worldwide, and addressing biodiversity loss.