Kathleen Erin Walsh is an American actress and businesswoman. She is best known for her role as Dr. Addison Montgomery in the ABC medical drama series Grey's Anatomy and Private Practice (2007–2013).

Addison Adrianne Forbes Montgomery, M.D., F.A.C.S., F.A.C.O.G. is a fictional character who appears as a supporting main character on the ABC television series Grey's Anatomy, and as the protagonist of its spin-off Private Practice played by Kate Walsh. Addison is a world-class neonatal surgeon with board certifications in both Obstetrics and Gynaecology and Maternal and Fetal Medicine. Additionally, she has completed a medical genetics fellowship. She works at the Oceanside Wellness Group, a fictional practice located in Santa Monica, California.