Margaret Sanger promised it would be “a miracle tablet.” Hugh Hefner hailed it as “a powerful weapon.” A 30-year-old woman with six children called it “my ray of hope.” The pill is now so common—four out of five sexually active women have used it—that it’s easy to forget that oral contraception was once the stuff of fantasy.

In The Birth of the Pill: How Four Crusaders Reinvented Sex and Launched a Revolution, Jonathan Eig chronicles the decades-long effort to make that fantasy a reality. In his telling, this transformation is thanks to a unique alliance between feminists and scientists: the spotlight-seeking activist Margaret Sanger, the rebel researcher Goody Pincus, the single-minded heiress Katherine McCormick, and the photogenic family doctor John Rock. These four people provide a formula for what it takes to create scientific breakthroughs that are ahead of their time politically: an incredible amount of drive and little concern for traditional values, a willingness to flout powerful institutions and their rewards, a tremendous amount of money, and, eventually, a way to appeal to the mainstream. It’s no wonder that, despite lots of modern talk about disruption and innovation, truly world-changing breakthroughs are so rare.

America before the pill sounds like something out of Margaret Atwood. Contraception was illegal in most states from 1873 until after World War I, and not even recognized by the American Medical Association until 1937. Single women in 26 states were denied contraception until well into the 1960s. While some women were lucky enough to live in a state with more liberal birth-control laws or near a clinic that was willing to circumvent them, many were out of luck. Women used douches as a dangerous and ineffective morning-after contraceptive. Some tried the rhythm method, but even doctors’ knowledge of the reproductive system was still spotty, so that technique wasn’t very effective. Condoms were available, but married couples were reluctant to use them. Some clinics offered diaphragms, which were often poorly fitted and difficult to obtain. And these methods were only available to women with male partners who were interested in preventing pregnancy. Many men were not.

As early as 1914, Margaret Sanger, then a women’s health activist in New York, had a crazy idea: reliable birth control—ideally in pill form so women’s partners wouldn’t even have to know they were taking it. It wouldn’t just ensure that “woman” was not synonymous with “mother,” it would be the dawn of a new era of women’s pleasure and self-realization: sex without fear of pregnancy. Sanger knew that as long as men had the final say in when and how women became mothers, they would have the final say about all aspects of women’s lives.

This was a long-term goal, though. In the meantime, Sanger founded the Birth Control Federation, later called Planned Parenthood, to distribute condoms and diaphragms and lobby for the liberalization of contraception laws. She became a figurehead. She fretted that talking about “family planning” instead of “birth control” would dilute her movement, yet seemed to have few qualms about cozying up to racist, eugenicist “population control” advocates in the hopes of spreading the birth control message wider and farther. But in the post-war era, as contraception became more accepted but still remained politically taboo, Sanger grew sick of the incremental approach. She did not want to focus on improving the diaphragm. She did not want to distribute more condoms. She wanted a pill...