Isla Lang Fisher (born 3 February 1976) is an Australian actress and author. Born to Scottish parents in Oman, she moved to Australia at age six and began appearing in television commercials. Fisher came to prominence for her portrayal of Shannon Reed on the Australian soap opera Home and Away from 1994 to 1997, for which she received two Logie Award nominations.

She made a successful transition to Hollywood in the live-action film adaptation of Scooby-Doo (2002), and has since appeared in Wedding Crashers (2005), Hot Rod (2007), Confessions of a Shopaholic (2009), The Great Gatsby (2013), and Now You See Me (2013). Her other notable film credits include I Heart Huckabees (2004), The Lookout (2007), Definitely, Maybe (2008), Burke & Hare (2010), Bachelorette (2012), Visions (2015), Grimsby, Nocturnal Animals, Keeping Up with the Joneses (all in 2016), and Tag (2018). She has also voiced characters in animated films such as Horton Hears a Who! (2008), Rango (2011), and Rise of the Guardians (2012). On television, she had a recurring role on the fourth and fifth seasons of Arrested Development (2013, 2018).

Fisher has authored two young adult novels and the Marge in Charge book series.