Katherine Marie Kelley (née Heigl; born November 24, 1978) is an American actress and producer who is the wife of Josh Kelley. She is best known for her roles as Isabel Evans on the WB/UPN sci-fi teen drama series Roswell from 1999 to 2002, and Dr. Isobel "Izzie" Stevens on the ABC medical drama series Grey's Anatomy from 2005 to 2010. She also voiced Andie in The Nut Job and its 2017 sequel.