The United States of America is the world’s largest national economy, representing 22.4% of nominal global GDP and 16.6% of global GDP (PPP).The United States’ GDP was estimated to be $17.555 trillion as of Q3 2014. The U.S. dollar is the currency most used in international transactions and is the world’s foremost reserve currency. Several countries use it as their official currency, and in many others it is the de facto currency. The United States has a mixed economy and has maintained a stable overall GDP growth rate, a moderate unemployment rate, and high levels of research and capital investment. Its six largest trading partners are Canada, China, Mexico, Japan, Germany, and South Korea.
The US has abundant natural resources, a well-developed infrastructure, and high productivity. It has the world’s ninth-highest per capita GDP (nominal) and tenth-highest per capita GDP (PPP) as of 2013. Americans have the highest average household and employee income among OECD nations, and in 2010 had the fourth highest median household income, down from second highest in 2007. It has been the world’s largest national economy (not including colonial empires) since at least the 1890s.
The U.S. is the world’s largest producer of oil and natural gas. It is the second-largest trading nation in the world as well as the world’s second largest manufacturer, representing a fifth of the global manufacturing output. Of the world’s 500 largest companies, 128 are headquartered in the US.