Ocean Conservancy (founded as The Delta Corporation) is a nonprofit environmental advocacy group based in Washington, D.C., United States. The organization seeks to promote healthy and diverse ocean ecosystems, prevent marine pollution, climate change and advocates against practices that threaten oceanic and human life.

The Ocean Conservancy was founded in 1972 by Bill Kardash as Delta Organization. Initially established to protest commercial whaling, the group launched their first initiative in 1978. The initiative was the Whale Protection Fund, which collected 500,000 signed petitions and presented them at the International Whaling Commission's annual meeting in London.

The organization's name was changed in 1975 to the Center for Environmental Education (CEE), shifting the focus to raising awareness about environmental and marine life conversation and issues. Recognizing the need for legislation to protect marine healthy and safe ocean ecosystems and to help prevent things that threaten oceanic and human life.

During the 1980s, the CEE expanded its focus to encompass broader goals of protecting ocean wildlife. This shift coincided with a significant development in 1982 when the International Whaling Commission imposed a ban on commercial whaling. Inspired by this milestone, the CEE started advocating for the conservation of various marine species and habitats. To further advance its mission, the organization launched the Marine Sanctuary Program in the 1986, and hosted the very first International Coastal Cleanup in 1986. Through this initiative, the organization actively lobbied for the creation of coastal wildlife preserves, seeking to establish protected areas that would safeguard and preserve critical marine ecosystems.

In 1989, CEE became the Center for Marine Conservation (CMC), and expanded it scope to address specific issues like overfishing, marine pollution, habitat destruction and unsustainable coastal development. In 2001, the organization was officially renamed the Ocean Conversancy. The conservancy's main concern was to restore sustainable American fisheries and protect wildlife from human impact.

The organization with the help of more than 19 million volunteers and employees, has enacted new initiatives and goals, including advocating for strong ocean policies, conducting scientific research, fostering collaborations, and empowering communities to protect and restore the health of oceans and coastal habitats.

After a four-year advocacy effort, the Ocean Conservancy helped enact a Congressional rewrite of the Magnuson–Stevens Fishery Conservation and Management Act in 1996, which changed how fisheries are managed. The act remains the nation's primary fisheries law. Before 1996 the law contained no provisions to stop overfishing or require the rebuilding of fish stocks. There was no prohibition of bycatch when fish and animals were caught unintentionally by fishing gear or nets targeting specific species. Nor was there a directive to protect fish habitats. The organization lobbied successfully to close these loopholes and establish more sustainable fishing practices.

The Ocean Conservancy aims to protect marine mammals and their habitats. In 1979, the organization established the Seal Rescue Fund (SRF) to protect marine mammals from commercial exploitation. Its efforts to ban whaling resulted in the International Whaling Commission adopting an international moratorium on commercial whaling in 1982. In 1984, Ocean Conservancy led efforts against the U.S.-sanctioned fur seal hunt by blocking the renewal of the North Pacific Fur Seal Treaty in the Pribilof Islands, as well as efforts to protect dolphins from the tuna industry. Ocean Conservancy also assisted in the creation of the dolphin-safe tuna-labeling program.