Eugenics entails using science and/or breeding techniques to produce individuals with preferred or "better" characteristics.

In the early twentieth century, eugenic ideologies and practices drew on genetic theories of the day in efforts to control human reproduction. This provided scientific cover for policy decisions about who should and shouldn't reproduce—decisions largely informed by discriminatory attitudes toward marginalized groups. In the United States, a widespread eugenics movement led to the forced sterilization of tens of thousands of people considered "unfit," to stringent immigration restrictions on undesired populations, and to public policies that encouraged "fitter families" to produce more children.

Eugenic ideas and rhetoric pioneered in the United States were taken up by the Nazis, who used them to justify their extermination of Jews, people with disabilities, and other groups. The Nazi genocides led to an almost complete rejection of eugenic ideas immediately after World War II.

In recent years, a small but disturbing number of scientists, scholars, and others have begun calling for "reconsideration." Some urge the development of inheritable genetic modification (changing the genes passed on to children) and the expanded use of selection technologies such as pre-implantation genetic diagnosis. Some support these technologies as a way to "seize control of human evolution." Others see them as an efficient, rapid means to produce "enhanced" children.

There are still some traditional eugenicists who focus on purported racial and group differences in intelligence and behavior. But many transhumanists and other eugenicists seek to differentiate their high-tech visions from earlier programs. They say that they reject the racism and government coercion that characterized various twentieth century eugenicists, and argue that market dynamics and individual choice will drive twenty-first century eugenics.