In 1973, Stein graduated magna cum laude from Harvard College, where she studied psychology, sociology, and anthropology. She then attended Harvard Medical School and graduated in 1979.
Stein practiced internal medicine for 25 years. She also served as an instructor of medicine at Harvard Medical School. She retired from practicing and teaching medicine in 2005 and 2006, respectively.
Stein supports the creation of sustainable infrastructure based on clean renewable-energy generation and sustainable-community principles to stop a growing convergence of environmental crises in water, soil, fisheries, and forests.
Stein proposes that the United States transition to 100% renewable energy by 2030.
She supports a national ban on fracking on the grounds that "cutting-edge science now suggests fracking is every bit as bad as coal".
She has spoken against nuclear energy, saying it "is dirty, dangerous and expensive, and should be precluded on all of those counts.
She has argued that moving away from fossil fuels will produce substantial savings in healthcare costs.
Stein says that climate change is a "national emergency" and calling it "a threat greater than World War II.
She has described the Paris Climate Agreement as inadequate, saying it will not stop climate change. She has said that she would "basically override" the agreement and create a more effective one.
Stein also contends that we are in a major extinction event, the sixth great extinction, and that we could see half of the world's life forms disappear in this century.
Stein supports the Great Sioux Nation's opposition to the Dakota Access Pipeline, and in September 2016 joined protesters in North Dakota. Both Stein and her running mate, Ajamu Baraka, are facing misdemeanor criminal charges for spray-painting bulldozers at the construction site of the pipeline.
Stein supports GMO labeling, a moratorium on new GMOs, and the phasing out of existing GMO foods, unless independent research "shows decisively that GMOs are not harmful to human health or ecosystems".
In 2016, Stein said NASA funding should be increased, arguing that by halving the military budget, more money could be directed towards "exploring space instead of destroying planet Earth.
In a Washington Post interview, Stein said that vaccines should be approved by a board that people can trust, and "people do not trust a Food and Drug Administration," or Centers for Disease Control and Prevention, "where corporate influence and the pharmaceutical industry has a lot of influence."
Stein voiced concern about wireless internet (Wi-Fi) in schools, saying, "We should not be subjecting kids' brains especially to that... and we don’t follow this issue in our country, but in Europe where they do, you know, they have good precautions about wireless.
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