Odyssey Marine Exploration, Inc. is an American company engaged in the salvage of deep-water shipwrecks. Odyssey salvaged the U.S. Civil War era shipwreck of the SS Republic in 2003 and recovered over 50,000 coins and 14,000 artifacts from the site nearly 1,700 feet deep. Odyssey has several shipwreck projects in various stages of development around the world, including the codenamed Black Swan Project.

Between 1998 and 2001, Odyssey Marine Exploration searched for HMS Sussex and stated that it had located the shipwreck off Gibraltar at a depth of 821 metres. The ship sank in a storm in 1694 during the War of the Grand Alliance as it was transporting 10 tons of gold coins to buy the allegiance of the Duke of Savoy, Victor Amadeus II, against France.

In September 2002, Odyssey reached an agreement with the British government on a formula for sharing any potential spoils, under which Odyssey would get 80 percent of the proceeds up to $45 million, 50 percent from $45 million to $500 million and 40 percent above $500 million. The British government would get the rest.

The company was poised to start the excavation in the late summer of 2003, according to the approved project plan and engaged Gifford and Partners to assist with archaeological aspects, but the project was delayed when Odyssey discovered and began excavating the SS Republic which continued until early 2003. The Sussex agreement was criticized by some archaeological organizations and charities, including the Council for British Archaeology, Rescue, and the Institute of Field Archaeologists, denouncing it as a dangerous precedent for the "ransacking" of shipwrecks by private firms under the aegis of archaeological research. An early day motion was signed by 60 British MPs condemning the treasure hunting.

In December 2005 Odyssey began archaeological investigation of the site believed to be HMS Sussex. The company adhered to the project plan submitted and accepted by the Sussex Archaeological Executive, a committee of archaeological consultants approved by the UK Government. As of 2009, Odyssey had completed Phase 1A (the non-disturbance survey) and a substantial portion of Phase 1B (trial excavation of the site believed to be HMS Sussex) to the satisfaction of the UK Government. Odyssey was authorized by HMG to complete phase 1B of the project.

Before Odyssey could complete Phase 1B of the Sussex project plan, it was stopped by the Spanish authorities, in particular the Junta of Andalusia in January 2006. In early June 2006, Odyssey provided clarification to Spain's Ministry of Foreign Affairs through the offices of the embassy of the United Kingdom. Odyssey then awaited final comments on the plan before resuming operations on the shipwreck believed to be that of the Sussex.

In March 2007, Andalusia gave its assent for the excavation to start with the condition that Spanish archaeologists take part in order to ascertain that the shipwreck to be excavated was indeed the Sussex and not a Spanish vessel. While waiting for Andalusia to appoint an archaeologist to participate in the Sussex expedition, the company began operations on the "Black Swan" salvage (see below) and since then, Spain has rescinded all cooperation with the company.

In May 2007, the company announced the salvage of 17 tons of mainly silver and some gold coins from a wreck in an undisclosed location "in international waters". The shipwreck was later proved to be that of the Spanish frigate Nuestra Señora de las Mercedes, which blew up and sank in the Action of 5 October 1804.

Following the discovery, Odyssey brought the coins and artifacts recovered into the jurisdiction of the United States Federal Court by filing an admiralty arrest pursuant to admiralty law. At that time, the Spanish government claimed that they believed the site was in Spanish territorial waters. The Spanish Government has since conceded that claim and sought to claim the discovered treasure based on their belief that the Nuestra Señora de las Mercedes should be afforded sovereign immunity.

On July 12, 2007, the Civil Guard seized the Odyssey Marine Exploration research vessel Ocean Alert 3.5 nautical miles (6 km) off the European coast. The Spanish Civil Guard claims to be responsible for customs control and European Union borders in this region, under the EU Schengen Agreement. This however, is disputed by the Government of Gibraltar and the UK Government who claim that the ship was detained in international waters near Gibraltar and that Spain therefore had no legal authority to board the vessel without the express consent of the flag state of the ship — in this case Panama. The Gibraltar Government stated that although this was a matter for the Government of Panama, they are "concerned that international shipping using Gibraltar port should be interfered with in this way in international waters."

The ship was ordered to sail to the Spanish port of Algeciras to undergo a search and inspection. Issues include the value and cultural significance of the shipwreck and the disputed status of Gibraltar between the UK and Spain. Panama is also involved because Odyssey's vessel is flagged there.

A U.S. federal judge awarded the treasure to Spain in December 2009, on the ground that the ship remained the property of Spain, but Odyssey appealed the ruling. Finally, after a five-year legal battle, in February 2012 the U.S. Supreme Court ordered Odyssey Marine to relinquish the treasure to Spanish authorities. Spain's culture minister indicated the treasure would be divided among several national museums. In September 2013, a U.S. district judge further ruled that Odyssey had acted in "bad faith", should have recognized Spain's right, and should thus reimburse $1 million in Spain's attorneys fees. Odyssey then issued a statement recognizing that this case was unusual and that the court ruling has clarified the applicable law, which Odyssey is committed to respecting.

In 2009, Odyssey Marine Exploration's searches were the subject of the Discovery Channel program, Treasure Quest.

In 2014, Odyssey Marine Exploration was selected to salvage gold from the 1857 shipwreck of the SS Central America.

Odyssey's stock price fell below $1 in 2014 and traded even lower in 2015.

In December 2015, Odyssey announced the sale of part of its assets to a company called Monaco Financials for $21 million. This capital allowed the company to reimburse a $11.7 million bank debt. Sold assets included the company's headquarters building in Florida, 50% of underwater mining business Neptune Minerals and a profit sharing agreement on future shipwreck salvages. CEO Mark Gordon also stated that the company would refocus on underwater mining, while treasure hunting would remain "part of the mix".