The American economy has had the fastest and most dramatic development of all the world's major economies. Four hundred years ago, the economic output of the area that became the United States was negligible by world standards. Yet only 250 years later, the U.S. economy had become the largest in the world, surpassing all other countries, including those that had a head start of thousands of years, such as China and Britain. The critical factor that explains America's exceptional growth is human creativity. The only force that could have enabled people to find productive uses for resources that had previously lain idle is knowledge. And knowledge has to be created by people--people known, in this role, as entrepreneurs. Entrepreneurs are the specialists who focus on innovation, developing new products and services and expanding the supply of resources that people can use to produce more of what they value. While it is not difficult to understand that entrepreneurs have created many improvements in the course of American history, it can be surprising to learn that they actually "founded" the U.S. economy. In this article, the author discusses the significant contributions of American entrepreneurs to the growth of the U.S. economy. (Contains 1 note.)