However, free enterprise is limited. Americans have always believed that some services are better implemented by public rather than private companies. For example, in the United States, the government is primarily responsible for justice, education (although there are many private schools and training centers), road systems, social statistics reports, and defense. In addition, the government is often required to intervene in the economy to correct the situation in which the price system does not work. For example, it regulates “natural monopoly,” which uses antitrust laws to control or break down other business combinations that become so powerful that they can go beyond market forces. The government has also solved the problem that market forces cannot match. It provides benefits and unemployment benefits for those who cannot support themselves because they have problems in their personal lives or have lost their jobs because of economic turmoil; it pays most of the medical expenses for the elderly and the poor; it regulates the private sector Limiting air and water pollution; it provides low-cost loans to people who suffer from natural disasters; it plays a leading role in space exploration, which is too expensive for any private company. In this mixed economy, individuals can not only help them as a consumer, but also help them guide the economy by voting for officials who make economic policies. In recent years, consumers have expressed concerns about product safety, environmental threats from certain industrial practices, and potential health risks that citizens may face; the government responds by establishing institutions that protect consumer interests and promote public welfare. The US economy has also changed in other ways. The population and labor force have been transferred from the farm to the city, from the field to the factory, and the most important is the transfer from the service industry. In today’s economy, providers of personal and public services far exceed the producers of agriculture and manufactured goods. As the economy becomes more complex, statistics also show a long-term trend of shifting from self-employment to working for others in the last century. This article is adapted from Conte and Carr’s “Introduction to the US Economy” and adapted from the US State Department.