For better or for worse, marriage today isn't what it used to be. According to a Pew Research Center analysis of U.S. Census Bureau data, just over half (51 percent) of American adults were married in 2011; in 1960, 72 percent had rings on their fingers.

It's also no longer for the young: In 1995, 59 percent of women were married by age 25, while between 2006 and 2010 only 44 percent in that age group had ever said "I do," according to the National Center for Health Statistics (NCHS). In 2010, the median age for first marriage was 25.8 for women and 28.3 for men — a steady rise since 1960, when the median age for both men and women was in the early 20s.

But while Americans are delaying marriage, they don't seem to be avoiding it altogether: NCHS found that women were just as likely to be married by age 40 between 2006 and 2010 as they were 1995. More and more seem to be opting for co-habitation earlier in life instead. Between 2006 and 2010, for example, 11 percent of unmarried women were living with a romantic partner, compared to just 3 percent in 1982.

Psychotherapist Nicholas Kirsch, PhD, who's been providing couples therapy in Bethesda, Md., for 25 years, says the changing face of marriage in America mirrors earlier trends in Europe. "There seems to be a kind of an organic, creative process around how people are forming relationships — or dissolving relationships," he says.

Whether that's a good or bad thing, he says, "is the million-dollar question."

—Anna Miller