The 20th century America was one of the major hubs of scientific and technological developments in the world. In the early part of the century, many prominent European scientists including Hans Bethe, Albert Einstein, Enrico Fermi, Leó Szilárd, Edward Teller, and Felix Bloch migrated to the United States where they accomplished several important achievements. During this era, scientists in the US made one highly controversial yet commendable accomplishment—the harnessing of nuclear energy. Gerald Woodrow Johnson, William Howard Arnold, and Charles Kincaid Bockelman were some of the established nuclear scientists of 20th century. America was also a pioneer in computer technology and information technology. Pioneers like John McCarthy who was one of the founders of the discipline of artificial intelligence played a major role in accelerating America’s progress in the area of computer science. Grace Brewster Murray Hopper, born in the early 20th century, was one of the first programmers of the Harvard Mark I computer. Americans have led the world in physics as well with the likes of Alan Harvey Guth, Steven Weinberg, and Sam Bard Treiman making important contributions to the field. Read on to learn more about the life and works of famous American scientists of the 20th century.