Graduated from North Hollywood High School in 1992.
Was a clarinet player in junior high school.
Played soccer until she got an injury in her early teens.
The producers of American Pie (1999) originally wanted her to play the role of Heather, but she wanted to play the role of Michelle because she thought it was funnier.
Has a tattoo of tribal dolphins on her ankle, and a japanese kanji, for luck and happiness, on her back.
She (along with actresses Tangi Miller and Holly Marie Combs) is a spokesperson for breast cancer, and will appear in a new four page brochure (to be featured in Vogue, Glamour, Self, Mademoiselle, and Women's Sports and Fitness) to raise awareness about the disease. [May 2000]
She co-starred in the television series "Free Spirit" (1989). The program was about a witch. Interestingly, she now plays a witch on the TV series, "Buffy the Vampire Slayer" (1997).
Married to Alexis Denisof. Denisof proposed during a trip to Northern California wine country during the 2002 holiday season. They were married in October 2003
At age 11 moved from Atlanta, Georgia, to Los Angeles
Her wedding was featured in the February 2004 issue of InStyle Magazine.
Has had two songs recorded about her: "Alyson Hannigan" by Juvenile Wreck, and "This One Time" (named for her famous "This one time, at band camp..." quotes from American Pie (1999)) by The Malcolm Effect.
Has worked with actor Jason Biggs four times - American Pie (1999), American Pie 2 (2001), American Wedding (2003), and Boys and Girls (2000).
She was invited to join the cast of the TV show In the Game (2005) (TV), but begged off, citing creative differences. Hannigan was supposed to play the best friend of the character played by Jennifer Love Hewitt, but according to a Knight Ridder/Tribune News Service interview reported January 25, 2005, she was unhappy with the diminished, trivialized role they presented her with. She chose to walk away from the offer.
Portrays the girlfriend of Seth Green's character in two different occasions. First was in the movie My Stepmother Is an Alien (1988) and then later in "Buffy the Vampire Slayer" (1997).
Owns a mansion in Sacramento, California.
Attended California State University in Northridge, California majored in Psychology