Alyson Lee Hannigan (born March 24, 1974) is an American actress. She is known for her roles as Willow Rosenberg in the television series Buffy the Vampire Slayer (1997–2003), Lily Aldrin on the CBS sitcom How I Met Your Mother (2005–present) and Michelle Flaherty in the American Pie film series (1999–present).
Hannigan was born in Washington, D.C. She is the only child of Emilie (Posner) Haas, a real estate agent, and Al Hannigan, a truck driver. Her father is of Irish descent and her mother is Jewish. Her parents divorced when she was two and she was raised mostly by her mother in Atlanta, Georgia.