This was a book I wrote in reaction to Lawrence Summers’ assertions about women in science back in 2005. At the time, Summers was the president of Harvard, where I was teaching but soon leaving to teach at CUNY. Even once I got to New York, people were abuzz about Summers’ comments—at least the ones suggesting that the dearth of women in science had something to do with their biological proclivities. Obviously, as a gender historian, I was intrigued by the controversy. Why did he seem to touch a collective nerve? I use the stories of twentieth-century women scientists to answer this question. My conclusion–that Summers exposed a truism few of us like to admit. Although many of us think women can be competent scientists, deep down, we also presume that women have to act like men to be them, which tells us that the problem of women in science is a deeply-seated CULTURAL one. From Marie Curie to Lillian Gilbreth, Harvard astronomers, Manhattan Project physicists, Nobel Prize winners and losers, and scientific popularizers like primatologists Jane Goodall and Dian Fossey, women scientists provide us with the best perspective on how the culture of American science has been shaped to appear masculine over time. I also explore the notions of ‘feminine’ and ‘feminist’ science in ways that will help women contemplating careers in science in the 21st century.