Modern Caltech grew from a vocational school founded in Pasadena in 1891 by local businessman and politician Amos G. Throop. The school was known successively as Throop University, Throop Polytechnic Institute, and Throop College of Technology, before acquiring its current name in 1920.

The driving force behind the transformation of Caltech from a school of arts and crafts to a world-class scientific center was the vision of astronomer George Ellery Hale. Hale had joined Throop's board of trustees after coming to Pasadena in 1907 as the first director of the Mount Wilson Observatory. At a time when scientific research in the United States was still in its infancy, Hale saw an opportunity to create in Pasadena an institution for serious research and education in engineering and the natural sciences. Hale succeeded in attracting private gifts of land and money that allowed him to endow the school with well-equipped, modern laboratory facilities. He then convinced two of the leading American scientists of the time, physical chemist Arthur Amos Noyes and experimental physicist Robert Andrews Millikan, to join Caltech's faculty and contribute to the project of establishing it as a center for science and technology.

Under the leadership of Hale, Noyes, and Millikan (and aided by the booming economy of Southern California), Caltech grew very significantly in prestige in the 1920's. In 1923, Millikan was awarded the Nobel Prize for physics. In 1925 the school established a department of geology and hired William Bennett Munro, then chairman of the division of History, Government, and Economics at Harvard University, to create a division of humanities and social sciences at Caltech. In 1928 a division of biology was established under the leadership of Thomas Hunt Morgan, the most distinguished biologist in the United States and a discoverer of the chromosome. In 1926 a graduate school of aeronautics was created which eventually attracted Theodore von Kármán, who later contributed to the creation of the Jet Propulsion Laboratory and who established Caltech as one of the foremost centers for rocket-science. In 1928 construction began on the Palomar Observatory.

Millikan served as "chairman of the executive council" (effectively Caltech's president) from 1921 to 1945, and his influence was such that the Institute was occasionally referred to as "Millikan's School." In the 1950's, 1960's, and 1970's, Caltech was known as the home of arguably the two greatest theoretical particle physicists working at the time: Murray Gell-Mann and Richard Feynman. Both Gell-Mann and Feynman received Nobel Prizes for their work, which was central to the establishment of the so-called "Standard Model" of particle physics. Feynman was also widely known outside the physics community as an exceptional teacher and a colorful, unconventional character.

Caltech remains, to this day, a relatively small university, with approximately 900 undergraduates, 1,200 graduate students, and 915 faculty members (including professors, permanent research faculty, and postdoctoral researchers.)

The movie comedy Real Genius was loosely based on events at Caltech. [1]