Fabien Cousteau (born 2 October 1967) is an aquanaut, ocean conservationist, and documentary filmmaker. As the first grandson of Jacques Cousteau, Fabien spent his early years aboard his grandfather's ships Calypso and Alcyone, and learned how to scuba dive on his fourth birthday. From 2000 to 2002, he was explorer-at-large for National Geographic and collaborated on a television special aimed at changing public attitudes about sharks called "Attack of the Mystery Shark". From 2003 to 2006, he produced the documentary Shark: Mind of a Demon that aired on CBS. With the help of a large crew, he created a 14-foot, 1,200-pound, lifelike shark submarine called Troy that enabled him to immerse himself inside the shark world.

For the next four years (2006–2010), Cousteau was part of a multi-hour series for PBS called Ocean Adventures with his father, Jean-Michel Cousteau, and sister, Céline, which was inspired by his grandfather's 1978 PBS series, Ocean Adventures.

In early 2009, Cousteau began working with local communities and children worldwide to help restore local water ecosystems. He continues to pursue these initiatives through the Fabien Cousteau Ocean Learning Center his non-profit 501(c)(3) founded in early 2016 dedicated to the restoration of the world's water bodies through active community engagement and education.

Fabien Cousteau is the grandson of oceanographic explorer Jacques Cousteau, and son of Jean-Michel Cousteau who assisted Jacques on most of his expeditions. Fabien was born and raised in France, although he has lived in the United States for most of his life. He has a sister, Céline Cousteau.

Fabien's first scuba dive was at age four when Jacques strapped a custom-made scuba tank to his back and sent the boy off into the Mediterranean Sea. His interest in sharks began at a young age, about 6 or 7, and was piqued when he sneaked into a showing of the film Jaws. The film perplexed him – "It went against everything I had ever learned about sharks ... Great white sharks don't go around chopping up boats," he explained – and started him on a mission to clear up "the gross misconceptions we have about sharks".

At age seven, Cousteau accompanied his grandfather and father on the first of many sea trips aboard the Calypso and Alcyone, the ships that transported the explorers to their dive locations. He officially joined the crew at age twelve; his first job was to remove barnacles from Jacques's boats.

Fabien attended Norfolk Academy in Virginia and graduated from Boston University with a bachelor's degree in environmental economics.

After school, Cousteau worked as a marketer for an American company, Seventh Generation. "I decided to start up in a different career, in which my name would not help me, just to see if I could survive", he explained. After three years, he returned to the family business, working for his father at Deep Ocean Odyssey, an exploration company founded by his grandfather.Fabien Cousteau found Technology living underwater." He then spent time as a diving and underwater product tester while looking for a company to appoint him "explorer-in-residence".