Rachel Sarah Bilson (born August 25, 1981) is an American actress. After growing up in a California show business family, she made her television debut in 2003 and subsequently became well-known for playing Summer Roberts on the prime time drama series The O.C. Bilson made her film debut in the 2006 film The Last Kiss, appeared as Lou on the NBC show Chuck, and starred in the 2008 action/sci-fi film Jumper.

Bilson was born in Los Angeles, California, the daughter of Janice (née Stango), a sex therapist, and Danny Bilson, a writer, director, and producer. Rachel Bilson's father is Jewish and her mother is a Philadelphia-born Italian American. Bilson's father comes from a show business family; her great-grandfather, George Bilson, (born in Leeds, Yorkshire, UK) was the head of the trailer department at RKO Pictures, while her Brooklyn-born great-grandmother, Hattie Bilson, was a screenwriter and her grandfather, Bruce Bilson, is a film director. Bilson's parents divorced during her childhood, and in 1997, her father remarried Heather Medway, an actress and the mother of Bilson's half-sister Hattie (born December 19, 2001).

Bilson has been noted as having a "self-destructive, rebellious period" during her teen years. When she was 16, she and a group of her brother's friends were involved in a car accident, a head-on collision with another car. As a result, Bilson was unconscious for a few days, had a scar above her right eye, and sometimes suffers from migraines and memory loss; she has stated that the experience "changed" her, encouraging her to "stop... getting into trouble" and stopping her from "going down that road".