From the Pew Forum on Religion and Public Life's U.S. Religious Landscape Survey report. The survey included 35,556 adults; interviews were done in English and Spanish from May 8 to Aug. 13, 2007. The numbers represented are percents.

Religious Diversity Is Growing in Society, and in Families

• The survey documents how immigration is adding religious diversity to the American population. For example, Muslims, roughly two-thirds of whom are immigrants, now account for roughly 0.6 percent of the U.S. adult population. Hindus, more than eight-in-ten of whom are foreign born, now account for approximately 0.4 percent of the population. While the number of Catholics born and raised in the U.S. is shrinking, immigration from majority Catholic countries in Central and South America is stabilizing the overall number of Catholics.
• Among people who are married, nearly four-in-ten (37 percent) are married to a spouse with a different religious affiliation. (This figure includes Protestants who are married to a Protestant from a different denomination, such as a Baptist who is married to a Methodist.)

Changing Religion Is Becoming More Common

• Constant movement characterizes the American religious marketplace, as every major religious group is simultaneously gaining and losing adherents. Those that are growing as a result of religious change are simply gaining new members at a faster rate than they are losing members.
• More than one-quarter of American adults (28 percent) have left the faith in which they were raised in favor of another religion—or no religion at all.
• Approximately one-third of the survey respondents who say they were raised Catholic no longer describe themselves as Catholic. This means that roughly 10 percent of all Americans are former Catholics.

Who Are the Religiously "Unaffiliated?"

• People not affiliated with any particular religion stand out for their relative youth compared with other religious traditions. Among the unaffiliated, 31 percent are under age 30. Among Americans ages 18-29, one-in-four say they are not currently affiliated with any particular religion.
• Although one-quarter of this group describe themselves as either atheist or agnostic (1.6 percent and 2.4 percent of the adult population overall, respectively), the majority of the unaffiliated population (12.1 percent of the adult population overall) is made up of people who simply describe their religion as "nothing in particular." This group, in turn, is fairly evenly divided between the "secular unaffiliated," that is, those who say that religion is not important in their lives (6.3 percent of the adult population), and the "religious unaffiliated," that is, those who say that religion is either somewhat important or very important in their lives (5.8 percent of the overall adult population).
• The number of people who say they are unaffiliated with any particular faith today (16.1 percent) is more than double the number who say they were not affiliated with any particular religion as children.