In 2017, approximately 39.7 million people, or 12.3% of the population, had incomes below the official definition of poverty in the United States. The poverty rate (the percentage that were in poverty), fell from 12.7% in 2016, while the number of persons in poverty showed no discernible change. In this report, the numbers and percentages of those in poverty are based on the Census Bureau's estimates. While this official measure is often regarded as a statistical yardstick rather than a complete description of what people and families need to live, it does offer a measure of economic hardship faced by the low-income population: the poverty measure compares family income against a dollar amount called a poverty threshold , a level below which the family is considered to be poor. The Census Bureau releases these poverty estimates every September for the prior calendar year. Most of the comparisons discussed in this report are year-to-year comparisons. This report only considers a number or percentage to have changed from the previous year, or to be different from another number or percentage, if the difference has been tested to be statistically significant at the 90-percent confidence level. However, in addition to the most recent year's data, this report presents a historical perspective as well as information on poverty for demographic groups (by family structure, age, race and Hispanic origin, and work status) and by state. Over the past several decades, criticisms of the official poverty measure have led to the development of an alternative research measure called the Supplemental Poverty Measure (SPM), which the Census Bureau also computes and releases. Statistics comparing the official measure with the SPM are provided at the conclusion of this brief. The SPM includes the effects of taxes and in-kind benefits (such as housing, energy, and food assistance) on poverty, while the official measure does not. Because some types of tax credits are used to assist the poor, as are other forms of assistance, the SPM may be of interest to policymakers. However, the official measure provides a comparison of the poor population over a longer time period, including some years before many current anti-poverty assistance programs had been developed. In developing poverty-related legislation and conducting oversight on programs that aid the low-income population, policymakers may be interested in these historical trends. The Census Bureau determines a person's poverty status by comparing his or her resources against a measure of need. For the official measure, "resources" is defined as total family income before taxes, and the measure of "need" is a dollar amount called a poverty threshold. There are 48 poverty thresholds that vary by family size and composition. If a person lives with other people to whom he or she is related by birth, marriage, or adoption, the money income from all family members is used to determine his or her poverty status. If a person does not live with any family members, his or her own income is used. Only money income before taxes is used in calculating the official poverty measure, meaning this measure does not treat in-kind benefits such as the Supplemental Nutritional Assistance Program (SNAP, formerly known as food stamps), housing subsidies, or employer-provided benefits as income. The poverty threshold dollar amounts vary by the size of the family (from one person not living in a family, to nine or more family members living together) and the ages of the family members (how many of the members are children under 18 and whether or not the family head is 65 years of age or older). Collectively, these poverty thresholds are often referred to as the "poverty line." As a rough guide, the poverty line can be thought of as $25,094 for a family of four, $19,515 for a family of three, $15,877 for a family of two, or $12,488 for an individual not living in a family, though the official measure is actually much more detailed. The threshold dollar amounts are updated annually for inflation using the Consumer Price Index. Notably, the same thresholds are applied throughout the country: no adjustment is made for geographic variations in living expenses. The official poverty measure used in this report is the federal government's definition of poverty for statistical purposes, such as comparing the number or percentage of people in poverty over time. A different definition of poverty, the poverty guidelines published by the Department of Health and Human Services (HHS), is used for administrative purposes such as eligibility criteria for assistance programs and will not be discussed in this report. Figure 1 shows a historical perspective of the number and percent of the population below the poverty line. The number in poverty and the poverty rates are shown from the earliest year available (1959) through the most recent year available (2017). Because the total U.S. population has grown over time, poverty rates are useful for historical comparisons because they control for population growth. Poverty rates fell through the 1960s. Since then, they have generally risen and fallen according to the economic cycle, though during the most recent two expansions poverty rates did not fall measurably until four to six years into the expansion. Historically notable lows occurred in 1973 (11.1%) and 2000 (11.3%) . Poverty rate peaks occurred in 1983 (15.2%), 1993 (15.1%), and 2010 (15.1%). Poverty rates tend to rise during and after recessions, as opposed to leading economic indicators such as new housing construction, whose changes often precede changes in the performance of the overall economy. The poverty rate's lag is explainable in part by the way it is measured: it uses income from the entire calendar year. Notably, the poverty rate in 2017 registered a third consecutive annual decrease since the most recent recession, though it remained higher than the rate in 2000, the most recent low point. The drop in the U.S. poverty rate (from 12.7% in 2016 to 12.3% in 2017) affected some demographic groups more than others, notably the population ages 18 to 64, people of Hispanic origin, and part-time workers; it was not a broad-based decline. Details for selected demographic groups are described below. Because poverty status is determined at the family level by comparing resources against a measure of need, vulnerability to poverty may differ among families of different compositions. In this section, poverty data by family structure are presented using the official poverty measure, along with a definition of "family" that the Census Bureau has used in the CPS ASEC for nearly four decades. In the " Supplemental Poverty Measure " section of this report, a different definition will be used. Families with a female householder and no husband present (female-householder families) have historically had higher poverty rates than both married-couple families and families with a male householder and no wife present (male-householder families). This remained true in 2017: female-householder families experienced a poverty rate of 25.7%, compared with 4.9% for married-couple families and 12.4% for male-householder families. None of these groups registered a significant decrease from 2016, although families as a whole (i.e., all family types together) did—from 9.8% in 2016 to 9.3% in 2017, a drop of 0.4 percentage points after rounding). Among individuals not living in families, the poverty rate was 20.7% in 2017, not distinguishable from the previous year. Poverty rates of families in 2017 are shown in Figure 2 . When examining poverty by age, three main groups are noteworthy for distinct reasons: under 18, 18 to 64, and 65 and older. People under age 18 are typically dependent on other family members for income, particularly young children below their state's legal working age. People ages 18 to 64 are generally thought of as the working-age population and typically have wages and salaries as their greatest source of income. People 65 years and older, referred to as the aged population, are often eligible for retirement, and those who do retire typically experience a change in their primary source of income. For the working-age population, the poverty rate, but not the number of persons in poverty (22.2 million), registered a decline. In 2017, 11.2% of the working-age population was in poverty (down from 11.6% in 2016). Neither children nor the aged registered any significant changes in their poverty rate or number in poverty from 2016. Among children, 12.8 million (or 17.5%) were poor; among the aged population, 4.7 million (or 9.2%) were poor. From a historical standpoint, the poverty rate for those 65 and over used to be the highest of the three groups. In 1966, the aged had a poverty rate of 28.5%, compared with 17.6% for those under 18 and 10.5% for working-age adults. By 1974, the poverty rate for people 65 and over had fallen to 14.6%, compared with 15.4% for people under 18 and 8.3% for working-age adults. Since then, people under 18 have had the highest poverty rate of the three age groups, as shown in Figure 3 . Poverty rates vary by race and Hispanic origin, as shown in Figure 4 . In surveys, Hispanic origin is asked separately from race; accordingly, people identifying as Hispanic may be of any race. The poverty rate fell for Hispanics (from 19.4% in 2016 to 18.3% in 2017). Among blacks (21.2%), Asians (10.0%), and non-Hispanic whites (8.7%), the poverty rate did not change discernably from 2016. While having a job reduced the likelihood of being in poverty, it did not guarantee that a person or his or her family would avoid poverty. Among the 18 to 64 year old population living in poverty, 36.6% had jobs in 2017. However, workers were less likely to be in poverty in 2017 (5.3%) than they were the year before (5.8%).