Haylie Katherine Duff (born February 19, 1985 in Houston, Texas) is an American actress and pop music singer who has appeared in several episodes of Lizzie McGuire, which stars her sister Hilary Duff. She has also appeared on another Disney Channel show, That's So Raven, and on other TV programs including Joan of Arcadia, American Dreams, Boston Public, and Chicago Hope. She wrote two songs for her sister's album, Metamorphosis, "Sweet Sixteen" and "Inner Strength", and she also sang with Hilary on a 2004 cover of The Go-Gos song, "Our Lips Are Sealed". She played a stereotypical popular teen girl named Summer in the 2004 independent film, Napoleon Dynamite. Haylie is currently landing the role of Sandy Jameson on 7th Heaven.

Her mother is the producer Susan Duff. Her father, Bob Duff, is a convenience store owner. She is also the older sister of Hillary Duff a singer now because of her.Haylie Duff influenced her younger sister to become a singer, just like her older sister.

Haylie has followed in her younger sister's footsteps (they both sing as well as act). She has sung songs for soundtracks like "Girl In The Band" (from The Lizzie McGuire Movie soundtrack), "A Whatever Life" (from the Stuck In The Suburbs soundtrack), and "One In This World" (from A Cinderella Story soundtrack). She also appears on the Family Guy: Live in Vegas soundtrack, an amusing duet with Stewie Griffin entitled "Babysitting Is A Bum Deal".