Alyson Lee Hannigan ( born March 24 , 1974 ) is an American actress and television presenter . She is best known for her roles as Willow Rosenberg on the television series '' Buffy the Vampire Slayer '' ( 1997 – 2003 ) , Lily Aldrin on the sitcom '' How I Met Your Mother '' ( 2005 – 2014 ) for which she won a People 's Choice Award in 2009 , and Michelle Flaherty in the '' American Pie '' film series ( 1999 – 2012 )
People 's Choice Award
36th People's Choice Awards
Alyson Hannigan