Margaret Ruth Kidder (born October 17, 1948, Yellowknife, Northwest Territories, Canada), better known as Margot Kidder, is a former popular and daring film actress of the 1970's and 1980's.

She is best known for her role as Lois Lane in the 1978 movie Superman and its sequels. Kidder brought more depth to the role than previous actresses had done, portraying Lane as an ambitious and headstrong, yet vulnerable and emotionally lonely woman trying to make it in a man's world. After she publicly expressed her disgust to the producers, Alexander Salkind and Ilya Salkind, over the firing of Richard Donner from 1980's Superman II, her role in 1983's Superman III consisted of less than 5 minutes of footage. Her presence was sorely missed by fans and moviegoers, and her role in 1987's Superman IV: The Quest For Peace was much more substantial.

Aside from the Superman franchise, Kidder has also starred in The Amityville Horror, Willie and Phil, The Great Waldo Pepper, and Black Christmas. She has made uncredited cameo appearances in Maverick and Delirious. In 1983, Kidder produced and starred (as Eliza Doolittle) in the TV version of Pygmalion with Peter O'Toole. She has also done extensive stage work, including The Vagina Monologues.

In 2005 Kidder briefly returned to the Superman franchise in two episodes of the television program Smallville as Dr. Bridgette Crosby, an emissary of Dr. Swann (played by her Superman co-star Christopher Reeve).

Kidder raised some hackles in the early 1990s during the U.S. intervention in Kuwait, when she ridiculed the press and the military for not seeing the larger consequences of their actions. Despite the criticism, Kidder became a United States citizen on August 17, 2005, in Butte, Montana; she lives in nearby Livingston). She said the reason for her decision to become an American citizen is to participate in the voting process, to continue her protests against U.S. intervention in Iraq and at the same time to be free of worries about being deported back to Canada.

Kidder has bipolar disorder which led to a widely publicized breakdown in 1996. She is now an advocate of orthomolecular medicine as a treatment for bipolar disorder. She admitted publicly that she has had an abortion in the past.