Married Love or Love in Marriage is a book by British academic Marie Stopes, first published in March 1918 by a small publisher, after many other larger publishers turned her down because of its controversial content. It rapidly sold out, and was in its sixth printing within a fortnight.

The US Customs Service banned the book as obscene until April 6, 1931, when Judge John M. Woolsey overturned that decision. Woolsey was the same judge who in 1933 would lift the ban on James Joyce's Ulysses, allowing for its publication and circulation in the United States of America.

It was the first book to note that women's sexual desire coincides with ovulation and the period right before menstruation. The book argued that marriage should be an equal relationship between partners. Although officially scorned in the UK, the book went through 19 editions and sales of almost 750,000 copies by 1931.

In 1935 a survey of American academics said Married Love was one of the 25 most influential books of the previous 50 years, ahead of Relativity by Albert Einstein, Interpretation of Dreams by Sigmund Freud, Mein Kampf by Adolf Hitler and The Economic Consequences of the Peace by John Maynard Keynes.

The book was the basis for a 1923 British silent film adaptation Married Love directed by Alexander Butler.

Marie Charlotte Carmichael Stopes (15 October 1880 – 2 October 1958) was a British author, palaeobotanist and campaigner for eugenics and women's rights.

She made significant contributions to plant palaeontology and coal classification, and was the first female academic on the faculty of the University of Manchester. With her second husband, Humphrey Verdon Roe, Stopes founded the first birth control clinic in Britain.

Stopes edited the newsletter Birth Control News, which gave explicit practical advice. Her sex manual Married Love (1918) was controversial and influential, and brought the subject of birth control into wide public discourse. Stopes opposed abortion, arguing that the prevention of conception was all that was needed.