In the United States, births to unmarried women (i.e., nonmarital births) are widespread, including families of varying income class, race, ethnicity, and geographic area. Many analysts attribute this to changed attitudes over many years about fertility and marriage. They find that many adult women and teenage girls no longer feel obliged to marry before, or as a consequence of, having children. During the period from 1940 to 2008, the percentage of births to unmarried women increased from 3.8% in 1940 to 40.6% in 2008, and has remained at about 41% each subsequent year through 2013. This represented 1.6 million children in 2013 (see Table A-1 . ). Although nonmarital childbearing is not a new phenomenon, the relatively recent factors associated with historically high levels of nonmarital childbearing are that women are marrying later in life and more couples are cohabiting. Other factors include decreased childbearing of married couples, increased marital dissolution, increased sexual activity outside of marriage, participation in risky behaviors that often lead to sex, improper use of contraceptive methods, and lack of marriageable partners. "Nonmarital births" can be first births, second births, or higher-order births; they can precede a marriage or occur to a woman who has never married. "Nonmarital births" can occur to divorced or widowed women. Moreover, a woman with several children may have had one or more births within marriage and one or more births outside of marriage. A majority of nonmarital births now are to cohabiting parents. Between 2006 and 2010, 58% of nonmarital births were to cohabiting parents, compared with 40% in 2002. Unlike in years past, although most of the children born outside of marriage are raised by a single parent (who may or may not have a "significant other"), many, especially during their infancy, live with both of their biological parents who are not married to each other. Parents and family life are the foundation that influences a child's well-being throughout the child's development and into adulthood. The family also is the economic unit that obtains and manages the resources that meet a child's basic needs while also playing an instrumental role in stimulating the child's cognitive, social, and emotional development. Most children who grow up in mother-only families, father-only families, step-parent families, or families in which the mother is cohabiting with a male partner become well-adjusted, productive adults. However, a large body of research indicates that children who grow up with only one biological parent in the home are more likely to be financially worse off and have worse socioeconomic outcomes (even after income differences are taken into account) compared to children who grow up with both biological parents in the home. To emphasize, this research indicates that all family situations in which both biological parents are not living together (regardless of whether the mother is divorced, separated, widowed, or was never married) are more likely to result in less favorable outcomes for children than a family situation in which the child is living in a household with both biological parents. It is also noteworthy that some researchers conclude that even among children living with both biological parents, living with married parents generally results in better outcomes for children than living with cohabiting parents, mainly because marriage is a more stable and longer lasting situation than cohabitation. In 2012, 70% of the children under age 18 who lived with both of their married parents were in households with incomes at least 200% above the poverty level, whereas 44%-46% of children who lived with their mother only, two unmarried parents, or no parents were living below the poverty level. The federal concern about nonmarital childbearing generally centers on its costs via claims on public assistance. These federal costs primarily reflect the fact that many of these "nonmarital children" are raised in single-parent families that are financially disadvantaged. Federal concern also arises because of the aforementioned research indicating that children living in single-parent families are more likely to face negative outcomes (financially, socially, and emotionally) than children who grow up with both of their biological parents in the home. As mentioned earlier, many children born outside of marriage are raised in single-parent families. This report analyzes the trends in nonmarital childbearing in the United States, discusses some of the characteristics of unwed mothers, addresses some issues involving the fathers of children born outside of marriage, and offers some concluding remarks. Declining marriage rates, increased childbearing among unmarried women, an increased number of unmarried women in the childbearing ages (i.e., 15-44), and decreased childbearing among married women have contributed to the rising share of children being born to unwed women. Many social science analysts attribute the increase in nonmarital births to the decades-long decline of "shotgun marriages," rather than to an increased incidence of nonmarital conceptions. They contend that when the social pressure to get married once pregnancy became obvious lessened, the likelihood that women would marry between conception and birth decreased substantially. The entry of more and more women into the paid labor force also made childbearing outside of marriage more economically feasible. Through the 1960s, most Americans believed that parents should stay in an unhappy marriage for the sake of the children. By the 1970s, this view was not as prominent. Divorce and not getting married to the father of a child—which were generally considered not to be in the best interest of the child—became more acceptable if they resulted in the happiness of the adult. Thus, many observers and analysts agree that marriage is now more likely to be viewed through a framework of adult fulfillment rather than through a framework of child well-being. On average, those who marry are marrying later. The age at which persons in the United States first marry has increased significantly since the 1950s. The typical age of first marriage in the United States is currently 27 for women and 29 for men. It is now not uncommon for first births to precede first marriage. The difference between the average age of first intercourse (17) and the age at first marriage (25) for women is eight years. For the majority of adult women, living without a spouse does not mean living without sex, nor in many cases does it mean living without having children. The report entitled "Knot Yet: The Benefits and Costs of Delayed Marriage in America," indicates that "at the age of 24, 44 percent of women have had a baby, while only 38 percent have married; by the time they turn 30, about two-thirds of American women have had a baby, typically out of wedlock." Cohabitation has now become a common method of family formation. Based on data covering the period 2006-2010, the first union of women (ages 15 through 44) was more likely to be cohabitation than marriage. According to the survey data, 48% of the women interviewed in 2006 through 2010 cohabited as a first union as compared to 23% who married as a first union (29% were single/unattached). The same survey data also indicated that by age 30, 74% of women had lived with a male partner without being married to him. According to a report entitled Household Change in the U nited States : One of the major trends driving the growth in nonfamily households with two or more people is the increase in cohabitation among unmarried adults. In 1970, less than 1 percent of all households included unmarried couples, yet by 2010, this share had increased to nearly 7 percent. This share may seem too low given that the majority of young adults today cohabit at some point, and that more than half of recent marriages were preceded by cohabitation. This apparent anomaly is due to the fact that most cohabiting unions in the United States don't last long, either transitioning to marriage or ending within a few years. Therefore, the number of unmarried-partner households counted at one point in time, such as in the 2010 Census, is relatively small. The long‐term trend toward nonmarital births may be attributed, in part, to an increase in cohabiting unions and in births within such relationships. According to several studies, a majority of nonmarital births now occur to cohabiting parents. During the period 2006-2010, it was estimated that 58% of nonmarital births were to cohabiting parents. Recent data indicate that the notion that unmarried births equal mother-only families is no longer fully correct. The decline in the percentage of births to married women has in large measure been in tandem with the increase in births to parents who are living together but who are not married (in cohabiting relationships). Some children live with cohabiting couples who are either their own unmarried parents or a biological parent and a live-in partner. The Census Bureau data do not indicate the number of newborns by the marital status of their parents, but data are available for children under age one by parents' marital status. In 2012, 16.7% of the 3.9 million children under age one were living with their biological mothers who had never married, 1.4% were living with their biological fathers who had never married, and 12.4% were living with both biological parents who were not married to each other (67.6% of those children under age one were living with both of their biological parents who were married to each other). Another view of the data indicates that of the 1.2 million children under age one who were living with parents who had never married or were not married to each other, 55.6% lived with their mothers, 4.6% lived with their fathers, and 39.8% lived with both parents.