If Knowlton was the first male propagandist for birth control in America, then Margaret Sanger was the first woman to be active in the same field. Her role in America has been compared to that of Marie Stopes in Britain. Mrs. Sanger was a declared socialist and took part in the various activities of the Labour movement. She marched with the "Wobblies" (The Industrial Workers of the World), and in 1914 began to publish a magazine called "The Woman Rebel," determined to make it as "red and flaming as possible." Apart from the "Rebel," Mrs. Sanger produced a small pamphlet called "Family Limitation".

It was soon announced that Mrs. Sanger had violated nine federal statutes; and under the Comstock regime, the man whose organisation, the New York Society for the Suppression of Vice made merry war against contraceptionists, she was prosecuted. She fled to England the day before the trial was due to be held. She met Marie Stopes and is said to have fallen in love with Havelock Ellis. Later she returned to America and lived through many tumultuous events.