Margaret Ruth "Maggie" Gyllenhaal (pronounced /ˈdʒɪlənhɑːl/; born November 16, 1977) is an American stage and screen actress. She is the daughter of director Stephen Gyllenhaal and screenwriter Naomi Foner Gyllenhaal (née Achs) and the older sister of actor Jake Gyllenhaal. She made her screen debut when she began to appear in her father's films. Gyllenhaal later achieved recognition in a supporting role in the indie cult hit Donnie Darko (2001). She made her break-through role in the 2002 sadomasochistic comedy Secretary, for which she received critical acclaim and a Golden Globe nomination.

Gyllenhaal has appeared in an eclectic range of films, including the indie film Sherrybaby (2006), for which she was nominated for a Golden Globe, the romantic comedy Trust the Man (2006) and big-budget films such as World Trade Center (2006) and The Dark Knight (2008). Gyllenhaal has also appeared in theatrical plays, including Closer (2000) and television productions including Strip Search (2004).

Gyllenhaal has been in a relationship with actor Peter Sarsgaard since 2002. In 2006, the two became engaged and Gyllenhaal gave birth to their daughter, Ramona, on October 3, 2006. On May 2, 2009 she and Sarsgaard were married in Italy. She is a politically active Democrat and, like her brother and parents, supports the American Civil Liberties Union. Prior to the US-led invasion of Iraq she participated in anti-war demonstrations. Gyllenhaal drew criticism in 2005 for her opinion that America was "responsible in some way" for the 9/11 attacks. She is actively involved in human rights, civil liberty and anti-poverty campaigns.