The California Institute of Technology (branded as Caltech) is a private research university/institute of technology in Pasadena, California, United States. The university is responsible for many modern scientific advancements and is among a small group of institutes of technology in the United States that are devoted to the instruction of pure and applied sciences.

The institution was founded as a preparatory and vocational school by Amos G. Throop in 1891 and began attracting influential scientists such as George Ellery Hale, Arthur Amos Noyes, and Robert Andrews Millikan in the early 20th century. The vocational and preparatory schools were disbanded and spun off in 1910, and the college assumed its present name in 1920. In 1934, Caltech was elected to the Association of American Universities, and the antecedents of NASA's Jet Propulsion Laboratory, which Caltech continues to manage and operate, were established between 1936 and 1943 under Theodore von Kármán.

Caltech has six academic divisions with strong emphasis on science and engineering, managing $332 million in research grants as of 2010. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles, in Pasadena. First-year students are required to live on campus, and 95% of undergraduates remain in the on-campus housing system at Caltech. Students agree to abide by an honor code which allows faculty to assign take-home examinations. The Caltech Beavers compete in 13 intercollegiate sports in the NCAA Division III's Southern California Intercollegiate Athletic Conference (SCIAC).

Scientists and engineers at or from the university have played an essential role in many modern scientific breakthroughs and innovations, including advances in space research, sustainability science, quantum physics, and seismology. As of October 2024, there are 80 Nobel laureates who have been affiliated with Caltech, making it the institution with the highest number of Nobelists per capita in America. This includes 48 alumni and faculty members (49 prizes, with chemist Linus Pauling being the only individual in history to win two unshared prizes). In addition, 68 National Medal of Science Recipients, 43 MacArthur Fellows, 15 National Medal of Technology and Innovation recipients, 11 astronauts, 5 Science Advisors to the President, 4 Fields Medalists, and 6 Turing Award winners have been affiliated with Caltech.