Seth Wilbur Moulton (born October 24, 1978) is an American politician serving as the U.S. representative for Massachusetts's 6th congressional district since 2015. A former Marine Corps officer, he is a member of the Democratic Party.

After graduating from Harvard University in 2001 with a Bachelor of Arts in physics, Moulton joined the United States Marine Corps. He served four tours in Iraq and then earned his master's degrees in business and public policy in a dual program at Harvard. He entered politics in 2014, when he was elected to represent Massachusetts's 6th congressional district.

In early 2019, Moulton was seen as a potential presidential candidate for the Democratic nomination in 2020. Publicly expressing his interest in the prospect, he traveled to early primary states. After announcing his candidacy on April 22, 2019, Moulton withdrew from the race on August 23.