Marriage is in trouble. Over the past half-century the number of single-parent households has skyrocketed to one-third of all U.S. families. The traditional American family structure appears to be crumbling.

President Bush and a growing marriage movement think it's time to take action. They are promoting marriage -- especially among the poor. Get people married, the thinking goes, and poverty will be reduced. Stem the tide of divorce and we'll solve many of society's ills. But is it that simple? Should the government have an activist role in personal relationships? And does marriage, in fact, really matter?

In "Let's Get Married," author and FRONTLINE correspondent Alex Kotlowitz explores these questions. "During my reporting, I became convinced that marriage, this most private of institutions, has very public consequences," Kotlowitz says. "And yet we have such a tough time talking about it. Why is that? This was kind of a personal journey for me -- an effort, in part, to answer that question -- and to figure out a way to talk about marriage and its critical place in our social framework."

"Let's Get Married" examines the social, political, and economic forces that have converged to advance the modern marriage movement -- an amalgam of Christian activists, political conservatives, and intellectuals.

The Bush administration has embraced the marriage movement's thinking. Stating that "stable families should be the central goal of American welfare policy," the president has proposed spending $300 million a year on experimental programs to encourage marriage.

The most extensive marriage experiment to date started in Oklahoma. Faced with the nation's second highest divorce rate, Gov. Frank Keating decided to take action, launching in 1999 a $10 million initiative to encourage people to think more carefully before making the decision to marry.

The documentary looks at how Keating's pro-marriage initiative is aimed at people like Johnni Dyer. Twice divorced, with four kids and no job, the 36-year-old Dyer lives in subsidized housing and is on welfare. To receive her welfare check, along with job training, Dyer now takes "PREP" -- the state's twelve-hour "relationship training" program. Although the classes have given Dyer a new perspective on her marriages, Dyer tells FRONTLINE that she really doesn't think the program would have saved her marriages.

While people in Oklahoma may be getting married -- and divorced -- too quickly, in some parts of America most people aren't getting married at all. Kotlowitz talks with couples and families in Chicago's inner-city neighborhoods, where just one in 10 babies is born to married parents. But he discovers a shift in the winds: according to a new in-depth study being conducted at Northwestern University, as part of a national survey on "fragile families," it seems that marriage is now at least being considered by most couples who have a child.

Yet the act of actually getting married remains rare in these Chicago neighborhoods. "Let's Get Married" profiles two young urban couples with children struggling with the decision of whether to marry. Ashaki Hankerson is 26 and has seven children by three different men. Like Johnni Dyer, she is also on welfare. She has never married. "I thought about marrying my oldest daughter's father, but we spent like ten years in and out of a relationship," Hankerson says. "He was kind of crazy. He was violent, really."

When viewers meet Hankerson, she has plans to marry Steven Thomas, the father of her youngest child. Thomas, however, is unemployed and looking for work.

Kathy Edin, director of the Northwestern University study, says she has seen many couples like Hankerson and Thomas. "What's interesting," she notes, "is the criteria they have for marriage." Edin says marriage has become an ideal for couples to aim for. "Marriage isn't something you do now, and then you work together as a couple to achieve your dream, the way it maybe was for our parents. Marriage is the finish line. It's the frosting on the cake. It's graduation."

That's an attitude most members of the marriage movement would like to change. Marriage proponents say that, statistically, children of divorced or never-married parents are far more likely to end up disadvantaged than children of two-parent households.

"Let's Get Married" traces the evolution of the public policy debate over marriage -- from Daniel Patrick Moynihan's explosive 1965 report on the erosion of the African-American family, to 1992, when Vice President Dan Quayle's criticism of TV character Murphy Brown's unwed pregnancy made headlines. But FRONTLINE's interviews with social scientists and researchers reveal how -- on both the right and the left -- there is a growing consensus that, all things being equal, two-parent families are best for children.

"I think the gulf between liberals and conservatives on family issues is closing," economist Ron Mincy says. "What we agree on is that there is a problem. Our children are not doing 'family' in ways that are going to promote the well-being of our grandchildren. What's not clear is what are we going to do about it?"

If the Bush administration has its way, government will soon take a more active role in promoting marriage. Later this year, Congress, in continuing the reform of welfare, will consider funding programs to promote marriage among the poor.

"Can government be the solution for everything that ails the American family? Of course not," says Bush administration official Wade Horn. "But I do think that we have moved beyond the question of whether government ought to be involved in some way on the issue of marriage, to the question of how."