U.S.-China economic ties have expanded substantially over the past three decades. Total U.S.- China trade rose from $2 billion in 1979 to $562 billion in 2013. China is currently the United States' second-largest trading partner, its third-largest export market, and its biggest source of imports. China is estimated to be a $300 billion market for U.S. firms (based on U.S. exports to China and sales by U.S.-invested firms in China). Many U.S. firms view participation in China's market as critical to staying globally competitive. General Motors (GM), for example, which has invested heavily in China, sold more cars in China than in the United States each year from 2010 to 2013. In addition, U.S. imports of low-cost goods from China greatly benefit U.S. consumers, and U.S. firms that use China as the final point of assembly for their products, or use Chinese made inputs for production in the United States, are able to lower costs. China is the largest foreign holder of U.S. Treasury securities (nearly $1.3 trillion as of June 2014). China's purchases of U.S. government debt help keep U.S. interest rates low. Despite growing commercial ties, the bilateral economic relationship has become increasingly complex and often fraught with tension. From the U.S. perspective, many trade tensions stem from China's incomplete transition to a free market economy. While China has significantly liberalized it's economic and trade regimes over the past three decades, it continues to maintain (or has recently imposed) a number of state-directed policies that appear to distort trade and investment flows. Major areas of concern expressed by U.S. policy makers and stakeholders include China's relatively poor record of intellectual property rights (IPR) enforcement and alleged widespread cyber economic espionage against U.S. firms by Chinese government entities; its mixed record on implementing its World Trade Organization (WTO) obligations; its extensive use of industrial policies (such as financial support of state-owned firms, trade and investment barriers, and pressure on foreign-invested firms in China to transfer technology in exchange for market access) in order to promote the development of industries favored by the government and protect them from foreign competition; and its policies to maintain an undervalued currency. Many U.S. policy makers argue that such policies negatively impact U.S. economic interests and have contributed to U.S. job losses.