Addison Montgomery is a fictional character from the television series Grey's Anatomy and its spin-off, Private Practice. She is portrayed by actress Kate Walsh and is known for her role as a skilled neonatal surgeon. Addison is characterized by her strong personality, complex relationships, and professional challenges throughout the series. Initially introduced as a love interest for Derek Shepherd, Addison's character evolves as she navigates her career and personal life. She eventually moves to Los Angeles to work at the Seaside Health and Wellness Center, where she faces new medical and ethical dilemmas while forming new relationships with colleagues and patients.