Estelle Louise Fletcher (born July 22, 1934) is an American actress.

Fletcher had her acting debut in the television series Yancy Derringer in 1958. She guest starred in the television series Wagon Train in 1959 before making her film debut in A Gathering of Eagles in 1963. In 1974, after a decade-long hiatus from acting in which she raised a family, Fletcher was cast in Robert Altman's Thieves Like Us. The following year, Fletcher gained international recognition for her performance as Nurse Ratched in the drama film One Flew Over the Cuckoo's Nest (1975), for which she won the Academy Award for Best Actress, BAFTA Award for Best Actress in a Leading Role and Golden Globe Award for Best Actress. She became only the third actress to ever win an Academy Award, BAFTA Award and Golden Globe Award for a single performance, after Audrey Hepburn and Liza Minnelli. Other notable film roles include Exorcist II: The Heretic (1977), Brainstorm (1983), Firestarter (1984), Flowers in the Attic (1987), 2 Days in the Valley (1996), and Cruel Intentions (1999).

Later in her career, Fletcher returned to television, appearing as Winn Adami in Star Trek: Deep Space Nine (1993–1999), as well as receiving Primetime Emmy Award nominations for her guest-starring roles in the television series Picket Fences (1996) and Joan of Arcadia (2004). In 2011–2012, she appeared in a recurring role on the Showtime television series Shameless as Frank Gallagher's foul-mouthed and hard-living mother who is serving a prison sentence for manslaughter. More recently, she portrayed the recurring role of Rosie on the Netflix series Girlboss (2017).