Lynne Cox (born 1957 in Boston, Massachusetts) is an American long-distance open-water swimmer and writer. In 1971, she and her teammates were the first group of teenagers to complete the crossing of the Catalina Island Channel in California. She has twice held the record for the fastest crossing of the English Channel (1972 in a time of 9 h 57 mins and 1973 in a time of 9h 36 mins). In 1975, Cox became the first woman to swim the 10 °C (50 °F), 16 km (10 mi) Cook Strait in New Zealand. In 1976, she was the first person to swim the Straits of Magellan in Chile, and the first to swim around the Cape of Good Hope in South Africa.

Cox is perhaps best known for swimming 2 h 5 mins in the Bering Strait on 7 August 1987, from the island of Little Diomede in Alaska to Big Diomede, then part of the Soviet Union, where the water temperature averaged around 43 to 44 °F (6 to 7 °C). At the time people living on the Diomede Islands - only 3.7 km (2.3 miles) apart - were not permitted to travel between them, although the Eskimo communities there had been closely linked until the natives of Big Diomede were moved to the Russian mainland after World War II. Her accomplishment a few years before the end of the Cold War earned praise from both US President Ronald Reagan and Soviet leader Mikhail Gorbachev.