Margaret Higgins Sanger Slee (September 14, 1879 – September 6, 1966) was an American birth control activist and the founder of the American Birth Control League (which eventually became Planned Parenthood). Although she was initially met with opposition, Sanger gradually won some support for getting women access to contraception. In her drive to promote contraception and negative eugenics, Sanger remains a controversial figure.

Sanger was born in Corning, New York. Her mother, Anne Purcell Higgins, was a devout Roman Catholic who went through 18 pregnancies (with 11 live births) before dying of tuberculosis and cervical cancer. Sanger's father, Michael Hennessy Higgins, earned his living "chiseling angels and saints out of huge blocks of white marble or gray granite for tombstones," and was also an activist for women's suffrage, free public education, and socialism. Sanger was the sixth of eleven children and spent much of her youth assisting in household chores and care of her younger siblings. Sanger attended Claverack College, a boarding school in Claverack for two years. Her sisters paid her tuition. Sanger returned home in 1896 following her fathers request to come home to nurse her mother. Her mother died March 31, 1896. Toward the end of the century the mother of one of her Claverack friends arranged for her to enroll at a nursing program at a hospital in White Plains, an affluent New York suburb. In 1902, Margaret Higgins married architect William Sanger and the couple settled in New York City. Sanger had developed tuberculosis as a result of the care of her ill mother and her own overwork, and the Sangers moved to Saranac, New York in the Adirondacks, for health reasons. In 1903, she gave birth to her first child, Stuart.

In 1912, after a fire destroyed the home that her husband had designed, Sanger and her family moved to New York City, where she went to work in the East Side slums of Manhattan. That same year, she also started writing a column for the New York Call entitled "What Every Girl Should Know." Distributing a pamphlet, Family Limitation, to women, Sanger repeatedly caused scandal and risked imprisonment by acting in defiance of the Comstock Law of 1873, which outlawed as obscene the dissemination of contraceptive information and devices.