The United States has the largest and most technologically powerful economy in the world. US GDP (nominal) was estimated at nearly US$17 trillion in 2013 or around 25% of global GDP. The United States is a major driver of the global economy and a world leader in terms of international trade and investment, research and development expenditure, stock market capitalisation and its share of large global corporations. In this market-oriented economy, private individuals and business firms make most of the decisions, and the federal and state governments buy needed goods and services predominantly in the private marketplace. US business firms enjoy greater flexibility than their counterparts in Western Europe and Japan in decisions to expand capital plant, to lay off surplus workers, and to develop new products. At the same time, they face higher barriers to enter their rivals’ home markets than foreign firms face entering US markets. US firms are at or near the forefront in technological advances, especially in computers and in medical, aerospace, and military equipment.