Gillian Leigh Anderson OBE (/ˈdʒɪliən/ JIL-ee-ən; born August 9, 1968) is an American actress. Her credits include the roles of FBI Special Agent Dana Scully in the series The X-Files, ill-fated socialite Lily Bart in Terence Davies's film The House of Mirth (2000), DSU Stella Gibson in the BBC/RTÉ crime drama television series The Fall, sex therapist Jean Milburn in the Netflix comedy drama Sex Education, and British Prime Minister Margaret Thatcher in the fourth season of Netflix drama series The Crown. Among other honors, she has won two Primetime Emmy Awards, two Golden Globe Awards, and four Screen Actors Guild Awards.

Born in Chicago, Anderson grew up in London, England, and Grand Rapids, Michigan. She graduated from The Theatre School at DePaul University in Chicago, then moved to New York City to further her acting career. After beginning her career on stage, she achieved international recognition for her role as FBI Special Agent Dana Scully on the American sci-fi drama series The X-Files. Her film work includes the dramas The Mighty Celt (2005), The Last King of Scotland (2006), Shadow Dancer (2012), Viceroy's House (2017) and two X-Files films: The X-Files: Fight the Future (1998) and The X-Files: I Want to Believe (2008). Other notable television credits include: Lady Dedlock in Bleak House (2005), Wallis Simpson in Any Human Heart (2010), Miss Havisham in Great Expectations (2011), Dr. Bedelia Du Maurier on Hannibal (2013–2015), Media on American Gods (2017), and Eleanor Roosevelt on The First Lady (2022).

Aside from film and television, Anderson has taken to the stage and received both awards and critical acclaim. Her stage work includes Absent Friends (1991), for which she won a Theatre World Award for Best Newcomer; A Doll's House (2009), for which she was nominated for a Laurence Olivier Award, and a portrayal of Blanche DuBois in A Streetcar Named Desire (2014, 2016), winning the Evening Standard Theatre Award for Best Actress and receiving a second Laurence Olivier Award nomination for Best Actress. In 2019, she portrayed Margo Channing in the stage production of All About Eve for which she received her third Laurence Olivier Award nomination.

Anderson has supported numerous charities and humanitarian organizations. She is an honorary spokesperson for the Neurofibromatosis Network and a co-founder of South African Youth Education for Sustainability (SAYes). She was appointed an honorary Officer of the Most Excellent Order of the British Empire (OBE) in 2016 for her services to drama.

She has resided in London since 2002, after earlier years divided between the United Kingdom and the United States.