Margaret Ruth Gyllenhaal (born November 16, 1977) is an American actress.

Gyllenhaal (pronounced ['dʒɪlənhɑl]) was born in New York City. She is the daughter of part-Swedish American director Stephen Gyllenhaal and Ashkenazi Jewish American writer / producer Naomi Foner, and the sister of actor Jake Gyllenhaal. The family are descendants of the Swedish noble Gyllenhaal family.

She is currently dating actor Peter Sarsgaard, who is also very close friends with her brother Jake and co-starred with him in Jarhead. Maggie also maintains a friendship with fellow actress (and Swede) Kirsten Dunst, who once dated Jake.

During high school, she attended a semester away program in Vershire, Vermont called The Mountain School. After graduating she attended Columbia University, and spent a summer studying at RADA.

Her first film roles were directed by her father: Waterland (1992), A Dangerous Woman (1993), and Homegrown (1998). After graduating from college she had a number of supporting roles, notably co-starring with her brother in Donnie Darko in 2001.

Her break-out role was in Secretary, which earned her widespread acclaim including a Golden Globe nomination. She has followed up with roles in Adaptation., John Sayles's Casa de los Babys and Mona Lisa Smile alongside Julia Roberts.

On April 24, 2003, she spoke at the University of North Carolina at Chapel Hill in her first college speaking engagement. Her comments focused on criticisms of the film industry and what her experience has been like thus far.

Gyllenhaal drew fire after an April 22, 2005 interview with cable news channel NY1 in which she suggested that the United States was somewhat responsible for the terrorist attacks of September 11, 2001. She stated, "I think America has done reprehensible things and is responsible in some way …."

She has modelled for Miu Miu, a branch of the Prada fashion house, and for Reebok.