For most of U.S. history, in most communities, such unions were taboo.
It was only 40 years ago — on June 12, 1967 — that the U.S. Supreme Court knocked down a Virginia statute that barred whites from marrying nonwhites. The decision also overturned similar bans in 15 other states.
Since that landmark Loving v. Virginia ruling, the number of interracial marriages has soared; for example, black-white marriages increased from 65,000 in 1970 to 422,000 in 2005, according to Census Bureau figures. Factoring in all racial combinations, Stanford University sociologist Michael Rosenfeld calculates that more than 7 percent of America's 59 million married couples in 2005 were interracial, up from less than 2 percent in 1970.
Coupled with a steady flow of immigrants from all parts of the world, the surge of interracial marriages and multiracial children is producing a 21st-century America more diverse than ever, with the potential to become less stratified by race.
"The racial divide in the U.S. is a fundamental divide. ... but when you have the 'other' in your own family, it's hard to think of them as 'other' anymore," Rosenfeld said. "We see a blurring of the old lines, and that has to be a good thing, because the lines were artificial in the first place."
The boundaries were still distinct in 1967, a year when the Sidney Poitier film "Guess Who's Coming to Dinner" — a comedy built around parents' acceptance of an interracial couple — was considered groundbreaking. The Supreme Court ruled that Virginia could not criminalize the marriage that Richard Loving, a white, and his black wife, Mildred, entered into nine years earlier in Washington, D.C.
But what once seemed so radical to many Americans is now commonplace.
Many prominent blacks — including Supreme Court Justice Clarence Thomas, civil rights leader Julian Bond and former U.S. Sen. Carol Moseley Braun — have married whites. Well-known whites who have married blacks include former Defense Secretary William Cohen and actor Robert DeNiro.
Last year, the Salvation Army installed Israel Gaither as the first black leader of its U.S. operations. He and his wife, Eva, who is white, wed in 1967 — the first interracial marriage between Salvation Army officers in the United States.
Opinion polls show overwhelming popular support, especially among younger people, for interracial marriage.
That's not to say acceptance has been universal. Interviews with interracial couples from around the country reveal varied challenges, and opposition has lingered in some quarters.
Bob Jones University in South Carolina didn't dropped its ban on interracial dating until 2000; a year later, 40 percent of the voters objected when Alabama became the last state to remove a no-longer-enforceable ban on interracial marriages from its constitution.
Taunts and threats, including cross burnings, still occur sporadically. In Cleveland, two white men were sentenced to prison earlier this year for harassment of an interracial couple that included spreading liquid mercury around their house.
More often, though, the difficulties are more nuanced, such as those faced by Kim and Al Stamps during 13 years as an interracial couple in Jackson, Miss.
Kim, a white woman raised on Cape Cod, met Al, who is black, in 1993 after she came to Jackson's Tougaloo College to study history. Together, they run Cool Al's — a popular hamburger restaurant — while raising a 12-year-old son and 10-year-old daughter in the state with the nation's lowest percentage (0.7) of multiracial residents.
The children are home-schooled, Kim said, because Jackson's schools are largely divided along racial lines and might not be comfortable for biracial children. She said their family triggered a wave of "white flight" when they moved into a mostly white neighborhood four years ago — "People were saying to my kids, 'What are you doing here?"'
"Making friends here has been really, really tough," Kim said. "I'll go five years at a time with no white friends at all."
Yet some of the worst friction has been with her black in-laws. Kim said they accused her of scheming to take over the family business, and there's been virtually no contact for more than a year.
"Everything was race," Kim said. "I was called 'the white devil."'
Her own parents in Massachusetts have been supportive, Kim said, but she credited her mother with foresight.
"She told me, 'Your life is going to be harder because of this road you've chosen — it's going to be harder for your kids,"' Kim said. "She was absolutely right."
Al Stamps said he is less sensitive to disapproval than his wife. He tries to be philosophical.
"I'm always cordial," he said. "I'll wait to see how people react to us. If I'm not wanted, I'll move on."
It's been easier, if not always smooth, for other couples.
Major Cox, a black Alabamian, and his white wife, Cincinnati-born Margaret Meier, have lived on the Cox family homestead in Smut Eye, Ala., for more than 20 years, building a large circle of black and white friends while encountering relatively few hassles.
"I don't feel it, I don't see it," said Cox, 66, when asked about racist hostility. "I live a wonderful life as a nonracial person."
Meier says she occasionally detects some expressions of disapproval of their marriage, "but flagrant, in-your-face racism is pretty rare now."
Cox — an Army veteran and former private detective who now joins his wife in raising quarter horses — longs for a day when racial lines in America break down.
"We are sitting on a powder keg of racism that's institutionalized in our attitudes, our churches and our culture that's going to destroy us if we don't undo it," he said.
In many cases, interracial families embody a mix of nationalities as well as races. Michelle Cadeau, born in Sweden, and her husband, James, born in Haiti, are raising their two sons as Americans in racially diverse West Orange, N.J., while teaching them about all three cultures.
"I think the children of families like ours will be able to make a difference in the world, and do things we weren't able to do," Michelle Cadeau said. "It's really important to put all their cultures together, to be aware of their roots, so they grow up not just as Swedish or Haitian or American, but as global citizens."
Meanwhile, though, there are frustrations — such as school forms for 5-year-old Justin that provide no option for him to be identified as multiracial.
"I'm aware there are going to be challenges," Michelle said. "There's stuff that's been working for a very long time in this country that is not going to work anymore."
The boom in interracial marriages forced the federal government to change its procedures for the 2000 census, allowing Americans for the first time to identify themselves by more than one racial category.
About 6.8 million described themselves as multiracial — 2.4 percent of the population — adding statistical fuel to the ongoing debate over what race really means.
Kerry Ann Rockquemore, a professor of African-American studies at the University of Illinois-Chicago, is the daughter of a black father and white mother and says she is asked almost daily how she identifies herself.
The surge in interracial marriage comes at "a very awkward moment" in America's long struggle with racism, she says.
"We all want deeply and sincerely to be beyond race, to live in a world where race doesn't matter, but we continue to see deep racial disparities," Rockquemore said. "For interracial families, the great challenge is when the kids are going to leave home and face a world that is still very racialized."
The stresses on interracial couples can take a toll. The National Center for Health Statistics says their chances of a breakup within 10 years are 41 percent, compared to 31 percent for a couple of the same race.
In some categories of interracial marriage, there are distinct gender-related trends. More than twice as many black men marry white women as vice versa, and about three-fourths of white-Asian marriages involve white men and Asian women.
C.N. Le, a Vietnamese-American who teaches sociology at the University of Massachusetts, says the pattern has created some friction in Asian-American communities.
"Some of the men view the women marrying whites as sellouts, and a lot of Asian women say, 'Well, we would want to date you more, but a lot of you are sexist or patriarchal,"' said Le, who attributes the friction in part to gender stereotypes of Asians that have been perpetuated by American films and TV shows.
Kelley Kenney, a professor at Kutztown University in Pennsylvania, is among those who have bucked the black-white gender trend. A black woman, she has been married since 1988 to a fellow academic of Irish-Italian descent. They have jointly offered programs for the American Counseling Association about interracial couples.
Kenney recalled some tense moments in 1993 when, soon after they moved to Kutztown, a harasser shattered their car window and placed chocolate milk cartons on their lawn. "It was very powerful to see how the community rallied around us," she said.
Kenney is well aware that some blacks view interracial marriage as a potential threat to black identity, and she knows her two daughters, now 15 and 11, will face questions on how they identify themselves.
"For older folks in the black community," she said "it's a feeling of not wanting people to forget where they came from."
Yet some black intellectuals embrace the surge in interracial marriages and multiracial families; among them is Harvard law professor Randall Kennedy, who addressed the topic in his latest book, "Interracial Intimacies: Sex, Marriage, Identity, and Adoption."
"Malignant racial biases can and do reside in interracial liaisons," Kennedy wrote. "But against the tragic backdrop of American history, the flowering of multiracial intimacy is a profoundly moving and encouraging development."