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. Caltech and the Polytechnic School, a private, college-preparatory school across the street, were part of the same institution until 1907.

Astronomer George Ellery Hale was a driving force in Caltech's growth to national prominence. 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.

In 1917 Hale hired architect Bertram Goodhue to produce a master plan for the 22-acre (89,000 m²) campus. Goodhue conceived of the overall layout of the campus and designed the Physics Building, Dabney Hall, and several other structures, in which he sought to be consistent with the local climate, the character of the school, and Hale's educational philosophy. Goodhue's designs for Caltech were also influenced by the traditional Spanish mission architecture of Southern California.


Under the leadership of Hale, Noyes, and Millikan (and aided by the booming economy of Southern California), Caltech grew to national prominence in the 1920s. 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 role of genes and the chromosome in heredity. In 1930, Kerckhoff marine laboratory was established in Corona del Mar under the care of Professor George MacGinitie. 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 1950s, 1960s, and 1970s, Caltech was known as the home of Murray Gell-Mann and Richard Feynman, whose work 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.

In 1971 a magnitude-6.5 earthquake in San Fernando caused some damage to the Caltech campus. Engineers who evaluated the damage determined that two historic buildings, Throop Hall and the Goodhue-designed Culbertson Auditorium, both dating from the early days of the Institute, had cracked. These were some of the first reinforced concrete buildings, and their plans did not contain enough details (such as how much reinforcing bar had been included in the concrete) to be sure they were safe, so the engineers recommended demolition. Unfortunately, the engineers were in error, and it required considerably more effort to demolish these historic structures than should have been necessary had they been in real danger of collapse. A large wrecking ball was used to demolish Throop Hall, and smashing the concrete revealed massive amounts of rebar, far in excess of safety requirements. The rebar had to be cut to haul the pieces away, and the process took much longer than had been planned.

Caltech remains, to this day, a small and highly focused university, with approximately 900 undergraduates, 1300 graduate students, and 900 faculty members (including 378 professors, 54 permanent research faculty, and 545 postdoctoral researchers.) It is a private institution, governed by its Board of Trustees.

As of 2005, Caltech claims 31 Nobel laureates to its name. This figure includes 17 alumni, 14 non-alumni professors, and 4 professors who were also alumni (Carl D. Anderson, Linus Pauling, William A. Fowler, and Edward B. Lewis). The number of awards is 32, because Pauling received prizes in both Chemistry and Peace. With fewer than 25,000 alumni in total, nearly one in a thousand Techers have received the Nobel Prize — a ratio unmatched by any other university. Five faculty and alumni have received a Crafoord Prize from the Royal Swedish Academy of Sciences, while 47 have been awarded the U.S. National Medal of Science, and 10 have received the National Medal of Technology *. Other distinguished researchers have been affiliated with Caltech as postdoctoral scholars (e.g., Barbara McClintock, James D. Watson, and Sheldon Glashow) or visiting professors (e.g., Albert Einstein and Edward Witten).

The movie comedy Real Genius and the CBS crime drama Numb3rs are loosely based on events at Caltech. *

Caltech is ranked tied for the fourth-best university (with MIT and Stanford) in the nation by the 2007 U.S. News & World Report*. Caltech is ranked seventh in the world in the 2006 The Times Higher Education Supplement, and sixth in the world in the 2006 Academic Ranking of World Universities*.

The Spitzer Science Center (SSC), located on the Caltech campus, is the data analysis and community support center for NASA's Spitzer Space Telescope. The SSC, part of the Infrared Processing and Analysis Center (IPAC), works in collaboration with the Jet Propulsion Laboratory.