The economy of the United States is the world's largest national economy. Its nominal GDP was estimated to be nearly $14.7 trillion in 2010,[1] approximately a quarter of nominal global GDP.[2][11] Its GDP at purchasing power parity was also the largest in the world, approximately a fifth of global GDP at purchasing power parity.[2] The U.S. economy also maintains a very high level of output per capita. In 2009, it was estimated to have a per capita GDP (PPP) of $46,381, the 6th highest in the world.

Historically, the U.S. economy has maintained a stable overall GDP growth rate, a low unemployment rate, and high levels of research and capital investment funded by both national and, because of decreasing saving rates, increasingly by foreign investors. It has been the world's largest national economy since the 1870s[12][13] and remains the world's largest manufacturer, representing 19% of the world's manufacturing output. In 2009, consumer spending, coupled with government health care spending constituted 70% of the American economy.[14] About 30% of the entire world's millionaire population reside in the United States (in 2009).[15] Furthermore, 34% of the world's billionaires are American (in 2011).[16][17] The US is also home to the world's largest stock exchange, the New York Stock Exchange. It also boasts the world's largest gold reserves and the world's largest gold depository, the New York Federal Reserve Bank. The United States is also home to 139 of the world's 500 largest companies, which is almost twice that of any other country.[18] A large contributor to the country's success has also been a very strong and stable currency. The US dollar holds about 60% of world reserves, as compared to its top competitor, the euro, which controls about 24%.

Since the 1960s, the United States economy absorbed savings from the rest of the world. The phenomenon is subject to discussion among economists. The US is by far the most heavily invested-into country in the world, with foreign investments made in the US measuring almost $2.4 trillion, which is more than twice that of any other country.[19] The US is also by far the largest investor in the world, with US investments in foreign countries totaling over $3.3 trillion, which is almost twice that of any other country.[20] Like other developed countries, the United States faces retiring baby boomers who have already begun withdrawing from their Social Security accounts; however, the American population is young and growing when compared to Europe or Japan. The United States public debt is in excess of $13 trillion and continues to grow at a rate of about $5.48 billion each day by direct calculation between Jan 31,2010 and August 31, 2010.[21] [22] Total public and private debt was $50.2 trillion at the end of the first quarter of 2010, or 3.5 times GDP.[23] Domestic financial assets totaled $131 trillion and domestic financial liabilities totaled $106 trillion.[24] Due in part to the amount of both public and private investment, the economy of the United States is regarded as a type of mixed economy.

The American labor market has attracted immigrants from all over the world and in 2009 ranked 16th in terms of net migration rate. The United States is ranked fourth, down from first in 2008-2009 due to the economic crisis, in the Global Competitiveness Report.[25] The country is one of the world's largest and most influential financial markets, home to major stock and commodities exchanges like NASDAQ, NYSE, AMEX, CME, and PHLX.