Roxanne Dunbar-Ortiz (born September 10, 1938) is an American historian, writer, professor, and activist based in San Francisco. Born in Texas, she grew up in Oklahoma and is a social justice and feminist activist. She has written numerous books including Blood on the Border: A Memoir of the Contra Years (2005), Red Dirt: Growing up Okie (1992), and An Indigenous Peoples' History of the United States (2014). She is professor emerita in Ethnic Studies at California State University.

Born in San Antonio, Texas, in 1938 to an Oklahoma family, Roxanne Dunbar-Ortiz grew up in Central Oklahoma. Her father was a sharecropper of Scots-Irish ancestry. Dunbar has written that her mother was of Cherokee descent and has said that her mother denied her Native ancestry after marrying into a white family. Because of her various claims of having Indigenous ancestry, Dunbar acknowledged that she has been "denounced as a fraud pretending to be Native American." In 2021, on C-SPAN2, she said: "I never had ties with anything. It’s pretty certain that probably my mother was not Cherokee. ... There’s no tracing it. ... I certainly would not call myself Cherokee.”

Dunbar's paternal grandfather was a settler, landed farmer, veterinarian, labor activist, and member of the Socialist Party in Oklahoma and the Industrial Workers of the World. Her father, Moyer Haywood Pettibone Scarberry Dunbar, was named after the leaders of the Industrial Workers of the World, "Big" Bill Haywood. Her father's stories of her grandfather inspired her to lifelong social justice activism. Her account of life up to leaving Oklahoma is recorded in the book Red Dirt: Growing Up Okie.

Married at 18, Dunbar-Ortiz and her husband moved to San Francisco three years later, where she has lived most of the years since. This marriage later ended. She has a daughter. She later married writer Simon J. Ortiz (Acoma Pueblo).

Dunbar-Ortiz graduated from San Francisco State College in 1963, majoring in history. She began graduate study in the Department of History at the University of California, Berkeley but transferred to the University of California, Los Angeles completing her doctorate in history there in 1974. In addition to the doctorate, she completed the Diplôme of the International Law of Human Rights at the International Institute of Human Rights, Strasbourg, France in 1983 and an MFA in creative writing at Mills College in 1993.

From 1967 to 1974, she was a full-time activist living in various parts of the United States, traveling to Europe, Mexico, and Cuba. She was also involved in the women's liberation movement. Outlaw Woman: Memoir of the War Years outlines this time of her life, chronicling the years 1960–1975.

In 1968 she founded Cell 16, which was a feminist organization in the United States known for its program of celibacy, separation from men, and self-defense training (specifically karate); it has been cited as the first organization to advance the concept of separatist feminism.

She contributed the piece "Female Liberation as the Basis for Social Revolution" to the 1970 anthology Sisterhood is Powerful: An Anthology of Writings From The Women's Liberation Movement, edited by Robin Morgan.