Addison Adrianne Forbes Montgomery (formerly Montgomery-Shepherd) is a board certified OB/GYN, subspecializing in maternal-fetal medicine (perinatology), a neonatal surgeon (one of the foremost in the country) and a medical geneticist at the Seaside Health and Wellness. She is married to Jake Reilly and mother to Henry Montgomery.

Addison attended medical school in New York where she met her future husband, Derek Shepherd.

Addison is entitled to a twenty five million dollar trust fund and owns three properties: a New York brownstone, a house in The Hamptons, and a house at Santa Monica. She now lives beside a beach in Malibu next door to an old friend, Sam Bennett.

Addison cheated on her husband of over 10 years, Derek with his best friend Mark Sloan. Prior to this, Addison and Derek's marriaged had been an unhappy one, as Derek had been putting in little effort. When he found Mark and Addison in bed together, he simply walked away. Derek then picked up his life in New York, sold his private practice, and relocated to Seattle. This is where he began his legendary relationship with Meredith Grey. Upon Richard's request to help out with a patient, Addison visited Seattle. When she arrived at the hospital, she noticed her husband, Derek talking to Meredith. She walked over and while he saw her doing so, Derek apologized to Meredith for what was to come. Addison then introduced herself as Derek's wife, about whom Meredith knew nothing.She and Derek tried to reconcile, and it worked well for a little bit, but it eventually ended in divorce.

Addison had very little in Seattle after she and Derek divorced. Her marriage with Derek was over, her relationship with Mark had completely vanished, and her attempt at a relationship with Alex Karev failed. She visited Los Angeles to see her friends Naomi and Sam Bennett. Naomi offered her a position at Oceanside Wellness Group and she accepted, thus relocating to Los Angeles.

Addison is a very confident, smart, and poised woman. She can be described as cold and unforgiving, however she is also quite warm and kind. She is also very concentrated and dedicated to her work, as she is considered the best in her field. Addison is sometimes difficult and uncompromising but she can be very kind and accepting.