In the United States, the concept of a working class remains vaguely defined, and classifying people or jobs into this class can be contentious. According to Frank Newport, "for some, working class is a more literal label; namely, an indication that one is working."

Economists and pollsters in the United States generally define "working class" adults as those lacking a college degree, rather than by occupation or income. Other definitions refer to those in blue-collar occupations, despite the considerable range in required skills and income among such occupations. Many members of the working class, as defined by academic models, are often identified in the vernacular as being middle-class, despite there being considerable ambiguity over the term's meaning.

Sociologists such as Dennis Gilbert and Joseph Kahl see the working class as the most populous in the United States, while other sociologists such as William Thompson, Joseph Hickey and James Henslin deem the lower middle class slightly more populous. In the class models devised by these sociologists, the working class comprises between 30% and 35% of the population, roughly the same percentages as the lower middle class. According to the class model by Dennis Gilbert, the working class comprises those between the 25th and 55th percentile of society. In 2018, 31% of Americans described themselves as working class. Retired American adults are less likely to describe themselves as "working class", regardless of the actual income or education level of the adult.

Since the 1970s, economic and occupational insecurity has become a major problem for American workers, their families, and their communities, to a much greater extent than their counterparts in peer countries. According to Matthew Desmond, the U.S. "offers some of the lowest wages in the industrialized world" which has "swelled the ranks of the working poor, most of whom are thirty-five or older." Jonathan Hopkin writes that the United States took the lead in implementing the neoliberal agenda in the 1980s, making it "the most extreme case of the subjection of society to the brute force of the market." As such, he argues this made the United States an outlier with economic inequality hitting "unprecedented levels for the rich democracies."

While outsourcing, the busting and decline of unionization and welfare supports, the rise of immigration, the prison-industrial complex, and unemployment have brought increased competition and considerable economic insecurity to working-class employees in the "traditional" blue-collar fields, there is an increasing demand for service personnel, including clerical and retail occupations. Sociologist Gosta Esping-Anderson describes these supervised service occupations as "junk jobs," as they fail to pay living wages in the face of asset and price inflation, fail to pay benefits, are often insecure, unstable, or temporary, and provide little work control and little opportunity for skill development or advancement. In contrast to other expensive countries with higher proportions of quality jobs, the U.S. has developed an economy where two-thirds of jobs do not require or reward higher education; the other one-third of jobs consist largely in managing the junk job workers. At the same time, political economist Radhika Desai says that working people have been encouraged, but not always permitted, to supplement their inadequate incomes with credit.

Despite, or perhaps because of the well-known limitations that the US labor market, inequality—including deep educational inequality, and other structural factors set on social mobility in the US, many commentators find more interesting the idea of class cultures. Education, for example, can pose an especially intransigent barrier in the US, and not just because of gross educational inequality; culture plays some role as well. The middle class is often recognized in the US by educational attainment, which is correlated with (but may not cause) income and wealth, especially for white men. Members of the working class commonly have a high school diploma and many have only some college education. Due to differences between middle and working class cultures, working class college students may face culture shock upon entering the post-secondary education system, with its "middle class" culture.

Labor historian Julie Greene writes that the working class of the United States is living through a Second Gilded Age "characterized by de-industrialization, the rise of the gig economy, and falling real wages." She distinguishes this from the original Gilded Age when working class people created powerful labor movements to improve wages and working conditions, whereas the second has seen a greater effort by the capitalist class and their supporters to roll back the labor movement and protections for workers, which has led to "greater acquiescence to exploitation." The disappearance of any alternatives to capitalism globally, in particular the dissolution of the Soviet Union and China's economic liberalization, she argues, has made this process easier.

Some experts, including the economists Anne Case and Angus Deaton and psychiatrist Anna Zeira, attribute rising diseases of despair, which are impacting mostly the working class, to what they see as flaws in contemporary capitalism: neoliberal capitalist policies which shifted political and economic power from labor to capital, (with an emphasis on cutting social services), weakened unions, and deregulated markets, which resulted in empowered corporations, increased outsourcing and rent-seeking, and increased economic inequality as wealth was transferred from the bottom to the top. Such policies, they argue, have been extremely toxic to the working class and have exacerbated emotional distress.