Rose Marie "Rosemary" Kennedy (September 13, 1918 – January 7, 2005) was the eldest daughter born to Joseph P. Kennedy Sr. and Rose Fitzgerald Kennedy. She was a sister of President John F. Kennedy and Senators Robert F. and Ted Kennedy.

Born on September 13, 1918, as a child, she reportedly exhibited developmental delays. In her young adult years, Kennedy was "becoming increasingly irritable and difficult." In response to these issues, her father arranged a lobotomy on her in 1941, when she was 23 years of age. The procedure left her permanently incapacitated and rendered her unable to speak intelligibly.

She spent most of the rest of her life being cared for at St. Coletta, an institution in Jefferson, Wisconsin. The truth about her situation and whereabouts was kept secret for decades. While she was initially isolated from her siblings and extended family following her lobotomy, she did go on to visit them during her later life. She then died on January 7, 2005.

Rose Marie Kennedy was born at her parents' home in Brookline, Massachusetts, on September 13, 1918. She was the third child and first daughter of Joseph P. Kennedy Sr. and Rose Fitzgerald. She was named after her mother and was commonly called Rosemary or Rosie. During her birth, the doctor was not immediately available because of an outbreak of the Spanish influenza epidemic, and the nurse ordered Rose Kennedy to keep her legs closed, forcing the baby's head to stay in the birth canal for two hours. The action resulted in a harmful loss of oxygen. As Rosemary began to grow, her parents noticed she was not reaching the basic developmental steps normally reached at a certain month or year. At two years old, she had a hard time sitting up, crawling, and learning to walk.

Accounts of Kennedy's life indicated that she had an intellectual disability, although some have raised questions about the Kennedys' accounts of the nature and scope of her disability. A biographer wrote that Rose Kennedy did not confide in her friends and that she pretended her daughter was developing typically, with relatives other than the immediate family knowing nothing of Rosemary's disability. Despite the help of tutors, Rosemary had trouble learning to read and write. At age 11, she was sent to a Pennsylvania boarding school for people with intellectual disabilities.

At age 16, Kennedy was sent to the Sacred Heart Convent in Elmhurst, Providence, Rhode Island, where she was educated separately from the other students. Two nuns and a special teacher, Miss Newton, worked with her all day in a separate classroom. The Kennedys gave the school a new tennis court for their efforts. Her reading, writing, spelling, and counting skills were reported to be at a fourth-grade level (ages 9–10). During this period, her mother arranged for her older brother John to accompany her to a tea dance. Thanks to him, she appeared "not different at all" during the dance.

Rosemary read few books, such as Winnie-the-Pooh. Diaries written by her in the late 1930s, and published in the 1980s, reveal a young woman whose life was filled with outings to the opera, tea dances, dress fittings, and other social interests. Kennedy accompanied her family to the coronation of Pope Pius XII in Rome in 1939. She also visited the White House. Kennedy's parents told Woman's Day that she was "studying to be a kindergarten teacher," and Parents was told that while she had "an interest in social welfare work, she is said to harbor a secret longing to go on the stage." When The Boston Globe requested an interview with Rosemary, her father's assistant prepared a response which Rosemary copied out laboriously:

I have always had serious tastes and understand life is not given us just for enjoyment. For some time past, I have been studying the well known psychological method of Dr. Maria Montessori and I got my degree in teaching last year.