Pieces of the story of Ann Dunham, the mother of Barack Obama, we know already. A “white woman from Kansas,” as he referred to her at the Democratic convention in 2008, who married an African intellectual and had a son with him. A strict mother who roused that son before dawn to study. An anthropologist who spent years studying in Indonesian villages, several of those years without her son. A 52-year-old woman whose last year before succumbing to cancer was spent in part trying to convince the Cigna insurance company that she should not be disqualified from benefits by virtue of a “pre-existing condition.” These are the parts of her life that resonate with our cultural anxieties about good mothering, access to health care and, of course, race.

We get a much fuller story of Ms. Dunham’s life in “A Singular Woman,” Janny Scott’s richly researched, unsentimental book. In it, we meet a very nonordinary woman, born Stanley Ann Dunham, “singular” from her naming onward. (“My father wanted a son,” she would say, “but he got me.”) Ann Dunham (she dropped the Stanley on graduating from high school) followed her peripatetic parents — a mother in banking and a father in furniture sales — through several states, to an island in Washington State, and finally on to Hawaii, where she met two husbands and got her B.A. and eventually her Ph.D. in anthropology.

While her times and her locations made her what she was to become — a Peace Corps-era optimist and a University of Hawaii East-West internationalist, for example — thanks to Ms. Scott, a former reporter for The New York Times, we see Ms. Dunham take a path more difficult than her peers’. The full fruits of the civil rights and women’s movements might have made some of her choices easier, but those would come only later. Ms. Dunham married a black man when roughly half of the United States outlawed such unions, and she had her children live with their grandparents for substantial periods while she worked abroad so that they could attend top American schools.

In telling Ms. Dunham’s transnational story, Ms. Scott uses a standard anthropological gambit: she first makes Kansas strange and then makes Indonesia — and the world of development experts in the 1970s and 1980s — familiar. Ms. Dunham’s family background was more varied, turbulent and unexpected than “Kansas” suggests: her ancestors’ livelihoods were affected by a huge oil strike in the state and war-industry boom and bust, as much as by farming, and they lived in a state where both Ku Klux Klansmen and pragmatic social reformers flourished.

And the Indonesia we encounter in the book is a world that includes the familiar comforts of family birthday parties and coffee with friends at day’s end. “The anonymity of urban America, even Honolulu, felt alien after the warmth and intimacy of Ann’s life in Jakarta,” Ms. Scott writes. She gives the stereotype of the anthropologist — a romantic in search of an exotic and disappearing world — a bit of a battering as well. Ms. Dunham first showed up in Indonesia in the immediate aftermath of the anti-Communist bloodbath of 1965-66 that killed a half million people across that country. Her Ph.D. thesis — a study of village blacksmithing that weighed in at a thousand pages — was less a catalog of ephemera and exotica than a description of a crucial strategy for making a living on the densely populated island of Java, where she made her home. Rather than attribute the problems of poverty in rural Indonesia to culture — to barriers of religious belief or lack of knowledge — she saw the problem as lack of access to capital and power. The book describes in detail how Ms. Dunham helped create and promote the micro-financing for poor entrepreneurs that is now a development mainstay.

She was, in a phrase, a community organizer.

Ms. Dunham’s love life over the years was intense, episodic and sometimes rocky. A virgin when she met the older, charismatic and confident Barack Obama Sr. in her first year at the University of Hawaii, she only later learned that he was already married to a Kenyan woman. He was one of a group of young Kenyans sent to be schooled in the United States in anticipation of his country’s independence.

She later met and fell in love with a kinder and more light-spirited man, an Indonesian named Lolo Soetoro, eventually an oil company liaison, with whom she had a second child. They later divorced over conflicting visions of what kind of life she could live as a woman and wife.

Ms. Scott’s visits with Ms. Dunham’s friends and family members (including the president) portray a generous person and a poor money manager, a heartfelt idealist and a sensible pragmatist, a free but disorganized spirit, a woman with deep love and admiration for her children. The author’s challenge, though, is that she realizes that most of her readers will want to know about the woman who made the president for the light her story sheds on him, not her. Ms. Scott resists, and so, in the end, the world of most of the book is Ms. Dunham’s personal life and work.

Most striking, though, is how much confidence and faith she had in her son from very early in his life. “She would boast about his brains, his achievements, how brave and bold he was,” Ms. Scott reports. More than one friend remembered her saying that she thought he could even be president of the United States. Yet for him to make a major mark on the world, Ms. Dunham knew he would need the educational opportunities of both life in another culture and the best prep school in Hawaii.

In the end, the book’s most moving passages come from President Obama himself, whom Ms. Scott interviewed a year and a half into his presidency. Despite the background role his mother plays in his memoir, “Dreams From My Father,” Mr. Obama says in “A Singular Woman” that she gave him “a sense of unconditional love that was big enough that, with all the surface disturbances of our lives, it sustained me, entirely.”

Not so paradoxically, it was his mother who gave him the bedrock belief that “beneath our surface differences, we’re all the same, and that there’s more good than bad in each of us. And that, you know, we can reach across the void and touch each other and believe in each other and work together.

“That’s precisely the naïveté and idealism that was part of her,” he added. “And that’s, I suppose, the naïve idealism in me.”